After upgrading my NCP RPi image on RPi3 to 1.50 today following by NextCloud 24.0.5 update, I encountered the similar issue.
The upgrade via nc-update in terminal took significantly longer this time. For a time being during compatibility plugin check-in, it appeared to be hang with little CPU and Disk usage for nearly 10mins. When I was about to take a look around on what went wrong, it proceeded automatically to next step. Then I noticed the system PHP7.4 was replaced by a PHP8.1 from 3rd party repo.
Anyway, the upgrade was completely in the end. I got Nextcloud 24.0.3 running. I could login via Web and access admin page. Below are what I did until it broke and gave me a 503.
Simply restarting php8.1-fpm doesn’t help at all though php binary itself is fine.
Nextcloud logs
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Check encryption key format","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Deprecated event type for \\OC\\Repair::step: Symfony\\Component\\EventDispatcher\\GenericEvent is used","userAgent":"--","version":"24.0.3.2","data":[]}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Remove old dashboard app config data","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Deprecated event type for \\OC\\Repair::step: Symfony\\Component\\EventDispatcher\\GenericEvent is used","userAgent":"--","version":"24.0.3.2","data":[]}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Add job to cleanup the bruteforce entries","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Deprecated event type for \\OC\\Repair::step: Symfony\\Component\\EventDispatcher\\GenericEvent is used","userAgent":"--","version":"24.0.3.2","data":[]}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Queue a one-time job to check for user uploaded certificates","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Deprecated event type for \\OC\\Repair::step: Symfony\\Component\\EventDispatcher\\GenericEvent is used","userAgent":"--","version":"24.0.3.2","data":[]}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Repair DAV shares","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Deprecated event type for \\OC\\Repair::step: Symfony\\Component\\EventDispatcher\\GenericEvent is used","userAgent":"--","version":"24.0.3.2","data":[]}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Add background job to set the lookup server share state for users","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"no app in context","method":"","url":"--","message":"Deprecated event type for \\OC\\Repair::step: Symfony\\Component\\EventDispatcher\\GenericEvent is used","userAgent":"--","version":"24.0.3.2","data":[]}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Repair::step: Repair step: Add token cleanup job","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:00+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Updater::startCheckCodeIntegrity: Starting code integrity check...","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:44+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Updater::finishedCheckCodeIntegrity: Finished code integrity check","userAgent":"--","version":"24.0.3.2","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:44+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Updater::updateEnd: Update successful","userAgent":"--","version":"24.0.5.1","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:44+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Updater::maintenanceDisabled: Turned off maintenance mode","userAgent":"--","version":"24.0.5.1","data":{"app":"updater"}}
{"reqId":"9IgSFbxtahfbGgaOTNOg","level":1,"time":"2022-09-24T02:41:44+00:00","remoteAddr":"","user":"--","app":"updater","method":"","url":"--","message":"\\OC\\Updater::resetLogLevel: Reset log level to Warning(2)","userAgent":"--","version":"24.0.5.1","data":{"app":"updater"}}
{"reqId":"Yy5xLO9tlbm-0z2VX0tLeQAABQg","level":3,"time":"2022-09-24T02:55:32+00:00","remoteAddr":"192.168.199.182","user":"ncp","app":"settings","method":"POST","url":"/settings/apps/enable","message":"could not enable apps","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:104.0) Gecko/20100101 Firefox/104.0","version":"24.0.5.1","exception":{"Exception":"GuzzleHttp\\Exception\\ConnectException","Message":"cURL error 28: Operation timed out after 120001 milliseconds with 0 bytes received (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://github.com/nextcloud/notes/releases/download/v4.5.1/notes.tar.gz","Code":0,"Trace":[{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","line":158,"function":"createRejection","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","line":110,"function":"finishError","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlHandler.php","line":47,"function":"finish","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::"},{"file":"/var/www/nextcloud/lib/private/Http/Client/DnsPinMiddleware.php","line":146,"function":"__invoke","class":"GuzzleHttp\\Handler\\CurlHandler","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/PrepareBodyMiddleware.php","line":35,"function":"OC\\Http\\Client\\{closure}","class":"OC\\Http\\Client\\DnsPinMiddleware","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Middleware.php","line":31,"function":"__invoke","class":"GuzzleHttp\\PrepareBodyMiddleware","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/RedirectMiddleware.php","line":71,"function":"GuzzleHttp\\{closure}","class":"GuzzleHttp\\Middleware","type":"::","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Middleware.php","line":63,"function":"__invoke","class":"GuzzleHttp\\RedirectMiddleware","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/HandlerStack.php","line":75,"function":"GuzzleHttp\\{closure}","class":"GuzzleHttp\\Middleware","type":"::","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Client.php","line":331,"function":"__invoke","class":"GuzzleHttp\\HandlerStack","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Client.php","line":168,"function":"transfer","class":"GuzzleHttp\\Client","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Client.php","line":187,"function":"requestAsync","class":"GuzzleHttp\\Client","type":"->"},{"file":"/var/www/nextcloud/lib/private/Http/Client/Client.php","line":218,"function":"request","class":"GuzzleHttp\\Client","type":"->"},{"file":"/var/www/nextcloud/lib/private/Installer.php","line":296,"function":"get","class":"OC\\Http\\Client\\Client","type":"->"},{"file":"/var/www/nextcloud/apps/settings/lib/Controller/AppSettingsController.php","line":448,"function":"downloadApp","class":"OC\\Installer","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":225,"function":"enableApps","class":"OCA\\Settings\\Controller\\AppSettingsController","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":133,"function":"executeController","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/App.php","line":172,"function":"dispatch","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/Route/Router.php","line":298,"function":"main","class":"OC\\AppFramework\\App","type":"::"},{"file":"/var/www/nextcloud/lib/base.php","line":1030,"function":"match","class":"OC\\Route\\Router","type":"->"},{"file":"/var/www/nextcloud/index.php","line":36,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","Line":210,"message":"could not enable apps","exception":{},"CustomMessage":"could not enable apps"}}
{"reqId":"Yy5x-xmoHfVti3vgE0ttGgAAVRg","level":3,"time":"2022-09-24T02:59:00+00:00","remoteAddr":"192.168.199.182","user":"ncp","app":"settings","method":"POST","url":"/settings/apps/enable","message":"could not enable apps","userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:104.0) Gecko/20100101 Firefox/104.0","version":"24.0.5.1","exception":{"Exception":"GuzzleHttp\\Exception\\ConnectException","Message":"cURL error 28: Operation timed out after 120000 milliseconds with 0 bytes received (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for https://github.com/nextcloud/notes/releases/download/v4.5.1/notes.tar.gz","Code":0,"Trace":[{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","line":158,"function":"createRejection","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","line":110,"function":"finishError","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlHandler.php","line":47,"function":"finish","class":"GuzzleHttp\\Handler\\CurlFactory","type":"::"},{"file":"/var/www/nextcloud/lib/private/Http/Client/DnsPinMiddleware.php","line":146,"function":"__invoke","class":"GuzzleHttp\\Handler\\CurlHandler","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/PrepareBodyMiddleware.php","line":35,"function":"OC\\Http\\Client\\{closure}","class":"OC\\Http\\Client\\DnsPinMiddleware","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Middleware.php","line":31,"function":"__invoke","class":"GuzzleHttp\\PrepareBodyMiddleware","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/RedirectMiddleware.php","line":71,"function":"GuzzleHttp\\{closure}","class":"GuzzleHttp\\Middleware","type":"::","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Middleware.php","line":63,"function":"__invoke","class":"GuzzleHttp\\RedirectMiddleware","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/HandlerStack.php","line":75,"function":"GuzzleHttp\\{closure}","class":"GuzzleHttp\\Middleware","type":"::","args":["*** sensitive parameters replaced ***"]},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Client.php","line":331,"function":"__invoke","class":"GuzzleHttp\\HandlerStack","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Client.php","line":168,"function":"transfer","class":"GuzzleHttp\\Client","type":"->"},{"file":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Client.php","line":187,"function":"requestAsync","class":"GuzzleHttp\\Client","type":"->"},{"file":"/var/www/nextcloud/lib/private/Http/Client/Client.php","line":218,"function":"request","class":"GuzzleHttp\\Client","type":"->"},{"file":"/var/www/nextcloud/lib/private/Installer.php","line":296,"function":"get","class":"OC\\Http\\Client\\Client","type":"->"},{"file":"/var/www/nextcloud/apps/settings/lib/Controller/AppSettingsController.php","line":448,"function":"downloadApp","class":"OC\\Installer","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":225,"function":"enableApps","class":"OCA\\Settings\\Controller\\AppSettingsController","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":133,"function":"executeController","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/AppFramework/App.php","line":172,"function":"dispatch","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->"},{"file":"/var/www/nextcloud/lib/private/Route/Router.php","line":298,"function":"main","class":"OC\\AppFramework\\App","type":"::"},{"file":"/var/www/nextcloud/lib/base.php","line":1030,"function":"match","class":"OC\\Route\\Router","type":"->"},{"file":"/var/www/nextcloud/index.php","line":36,"function":"handleRequest","class":"OC","type":"::"}],"File":"/var/www/nextcloud/3rdparty/guzzlehttp/guzzle/src/Handler/CurlFactory.php","Line":210,"message":"could not enable apps","exception":{},"CustomMessage":"could not enable apps"}}
EDIT: Provide more details on what had been done before it broke.