"Cannot connect securely... The Issuer certificate could not be found"

Nextcloud version: 27.1.1
Operating system and version: Client: Windows 10 Pro 19045.3448,
Server: unRAID 6.9.2 2021-04-07,
Docker 20.10.5
nginx version: 1.19.9 (I think)
PHP version: 7.4.26

The issue you are facing:
Desktop client, after update fails to connect to server with this error:

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

  1. Launch nextcloud desktop app for windows.

The output of your Nextcloud log in Admin > Logging:

[no app in context] Error: OCP\Http\Client\LocalServerException: Host violates local access rules at <<closure>>

 0. /app/www/public/lib/private/Http/Client/Client.php line 295
    OC\Http\Client\Client->preventLocalAddress()
 1. /config/www/nextcloud/apps/integration_homeassistant/lib/Service/HassIntegrationService.php line 29
    OC\Http\Client\Client->post()
 2. /config/www/nextcloud/apps/integration_homeassistant/lib/Dashboard/TemplateWidget.php line 65
    OCA\HassIntegration\Service\HassIntegrationService->getWidgetItems()
 3. /config/www/nextcloud/apps/integration_homeassistant/lib/Dashboard/TemplateWidget.php line 54
    OCA\HassIntegration\Dashboard\TemplateWidget->getItems()
 4. /app/www/public/lib/private/Dashboard/Manager.php line 114
    OCA\HassIntegration\Dashboard\TemplateWidget->load()
 5. /app/www/public/lib/private/Dashboard/Manager.php line 138
    OC\Dashboard\Manager->loadLazyPanels()
 6. /config/www/nextcloud/apps/dashboard/lib/Controller/DashboardApiController.php line 85
    OC\Dashboard\Manager->getWidgets()
 7. /config/www/nextcloud/apps/dashboard/lib/Controller/DashboardApiController.php line 130
    OCA\Dashboard\Controller\DashboardApiController->getShownWidgets()
 8. /app/www/public/lib/private/AppFramework/Http/Dispatcher.php line 230
    OCA\Dashboard\Controller\DashboardApiController->getWidgetItemsV2()
 9. /app/www/public/lib/private/AppFramework/Http/Dispatcher.php line 137
    OC\AppFramework\Http\Dispatcher->executeController()
10. /app/www/public/lib/private/AppFramework/App.php line 183
    OC\AppFramework\Http\Dispatcher->dispatch()
11. /app/www/public/lib/private/Route/Router.php line 315
    OC\AppFramework\App::main()
12. /app/www/public/ocs/v1.php line 64
    OC\Route\Router->match()
13. /app/www/public/ocs/v2.php line 23
    require_once("/app/www/public/ocs/v1.php")

GET /ocs/v2.php/apps/dashboard/api/v2/widget-items?widgets%5B%5D=activity
from 192.168.1.1 by USER1 at 2023-09-23T04:50:52+00:00

This is the only recurring error that shows up recently.

The output of your config.php file in /path/to/nextcloud:

<?php
$CONFIG = array (
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'datadirectory' => '/data',
  'instanceid' => '-',
  'passwordsalt' => '-',
  'secret' => '-',
  'trusted_domains' => 
  array (
    0 => 'x.x.x.x:444',
  ),
  'dbtype' => 'mysql',
  'version' => '27.1.1.0',
  'overwrite.cli.url' => 'https://cloud.-.com',
  'dbname' => 'nextcloud',
  'dbhost' => 'x.x.x.x:3306',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'Nextcloud',
  'filesystem_check_changes' => 0,
  'dbpassword' => '-',
  'installed' => true,
  'theme' => '',
  'loglevel' => 2,
  'maintenance' => false,
  'mail_smtpmode' => 'smtp',
  'mail_smtphost' => 'smtp.gmail.com',
  'mail_sendmailmode' => 'smtp',
  'mail_smtpsecure' => 'ssl',
  'mail_smtpport' => '465',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_from_address' => 'x',
  'mail_domain' => 'gmail.com',
  'mail_smtpname' => 'x',
  'mail_smtppassword' => 'x',
  'app_install_overwrite' => 
  array (
    0 => 'files_3d',
  ),
  'filelocking.enabled' => 'true',
  'memcache.locking' => '\\OC\\Memcache\\APCu',
);

The output of your Apache/nginx/system log in /var/log/____:
There is no content in error.log in the location above inside my docker.

Troubleshooting steps I have tried:
-repair install
-uninstall client completely and reinstall
-uninstall client and install previous version
-update Nextcloud server (Originally on v25.?)
-check ssl status of my domain: results Seems good in my limited understanding.

I use NginxProxyManager.
I’ve used it for the past few years with no issues, and it shows my certs for this subdomain as up to date and not expiring.
I recently changed my domain registrar, but this issue existed prior to that change.

I’d love a little guidance on this one- certs are a weak spot for me, and all my other clients continue to function (android and desktop on another machine).

Which client version are you using?

I tried 3.10.0 and 3.9.1.

Allowing 3.9.1 to update back to 3.10.0 seems to have fixed this issue.
Possibly due to a new flow for authentication?
Regardless, glad to have it resolved.