Difficulties with Pretty URLs and PHP 7.4

I need your help because I have no more ideas. I have been using Pretty URLs with PHP 7.3 for a long time, and it works perfectly. However, when I try to switch to PHP 7.4 I get an error message.

Nextcloud version: 20.0.7
Operating system and version: Ubuntu 18.04.3
Plesk: Obsidian 18.0.33 ,
PHP version: 7.4.15

Error message:

Internal Server Error
The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times, please include the technical details below in your report.
More details can be found in the server log.

Plesk-php74-fpm error log:

[23-Feb-2021 21:31:11] WARNING: [pool mydomain.net] child 6480 said into stderr: "NOTICE: PHP message: PHP Fatal error:  Uncaught Error: Class 'OCA\DAV\Connector\Sabre\ExceptionLoggerPlugin' not found in /var/www/vhosts/mydomain.net/mydomain.net/remote.php:61"
[23-Feb-2021 21:31:11] WARNING: [pool mydomain.net] child 6480 said into stderr: "Stack trace:"
[23-Feb-2021 21:31:11] WARNING: [pool mydomain.net] child 6480 said into stderr: "#0 /var/www/vhosts/mydomain.net/mydomain.net/remote.php(169): handleException()"
[23-Feb-2021 21:31:11] WARNING: [pool mydomain.net] child 6480 said into stderr: "#1 {main}"
[23-Feb-2021 21:31:11] WARNING: [pool mydomain.net] child 6480 said into stderr: "  thrown in /var/www/vhosts/mydomain.net/mydomain.net/remote.php on line 61"

I could not find any other “useful” error log. Does anyone have an idea how I can solve this problem?

There are a few remarks in this error report that show similar errors: Class 'OCA\DAV\Connector\Sabre\ExceptionLoggerPlugin' not found · Issue #5043 · nextcloud/server · GitHub

What sometimes is an issue, the new php 7.4 is not fully installed (with all required modules: Installation on Linux — Nextcloud latest Administration Manual latest documentation) or not everything is turned on and configured.

You were right. I had forgotten to install the memcached extension for PHP 7.4. :woozy_face: