HI @BeckeBauer, thanks for reaching out. It's hard to know what is happening based on that error message, it's meant to be shown when the login session could not be verified. Could you describe in detail what happens when you try to activate a plugin? When you try to activate the plugin are you shown a 'confirm password' prompt?

It could also be worth checking the diagnostics page to see if there are any warnings or errors with the new server configuration.

When I try to activate a deactivated plugin or vice versa, I get the white page with An error occurred Not available Go back - Go to Matomo without any "confirm password prompt"

When I run the diagnostics within matomo, the only error shown is Unable to execute check for https://mydomain.local/tmp/: curl_exec: SSL certificate problem: unable to get local issuer certificate. Hostname requested was: mydomain.local
(I use matomo to analyse the server logs and do not need it to be accessible from the internet so that I use a self-signed certificate)

When I try to run the diagnostics via console, I get the following error
ERROR [2022-05-20 08:58:02] 3645 Uncaught exception: /matomo/vendor/symfony/console/Symfony/Component/Console/Application.php(549): Command "generate:system-check" is not defined.

@BeckeBauer The commands for running the system checks would be diagnostics:run

sorry, was not aware of the right command. I got the following result:

INFO [2022-05-20 19:13:25] 3111  Unable to test if mod_pagespeed is enabled: the request to http://unknown/console?module=Installation&action=getEmptyPageForSystemCheck failed
Required Private Directories:
	- WARNING Unable to execute check for https://tracking.tracking.mydomain.local/config/config.ini.php: curl_exec: Could not resolve host: matomo.mydomain.local. Hostname requested was: matomo.mydomain.local
	- WARNING Unable to execute check for https://tracking.tracking.mydomain.local/tmp/cache/tracker/matomocache_general.php: curl_exec: Could not resolve host: matomo.mydomain.local. Hostname requested was: matomo.mydomain.local
	- OK All private directories are inaccessible from the internet.
Recommended Private Directories:
	- WARNING Unable to execute check for https://tracking.tracking.mydomain.local/tmp/: curl_exec: Could not resolve host: matomo.mydomain.local. Hostname requested was: matomo.mydomain.local
	- WARNING Unable to execute check for https://tracking.mydomain.local/tmp/empty: curl_exec: Could not resolve host: matomo.mydomain.local. Hostname requested was: matomo.mydomain.local
	- WARNING Unable to execute check for https://tracking.mydomain.local/lang/en.json: curl_exec: Could not resolve host: matomo.mydomain.local. Hostname requested was: matomo.mydomain.local
	- OK All private directories are inaccessible from the internet.
Forced SSL Connection: WARNING We recommend using Matomo over secure SSL connections only. To prevent insecure access over http, add force_ssl = 1 to the General section in your Matomo config/config.ini.php file.

Attention: Doing this without having set up a SSL certificate for using HTTPS will break Matomo.
3 warnings detected

@BeckeBauer I don't think those warnings should cause your problems.
Does enabling the plugin on command line work? e.g. ./console plugin:activate LogViewer

works flawless this way

/web/matomo$console plugin:activate LogViewer
Activated plugin LogViewer

I noticed that actions requiring password confirmation seems not to work. For instance, when I try to change my password (which is not working), the error log shows:

Uncaught exception: /web/matomo/core/Nonce.php(236): Security token could not be verified. [Query: ?module=UsersManager&action=recordPasswordChange&idSite=7&period=day&date=yesterday&embed=0&activated=, CLI mode: 0]

@BeckeBauer Which version of Matomo are you using and are you maybe using any additional login plugins?

I`ve been using the official release channel, currently vers. 4.10.1
But I gave up and installed a clean database (I assume that something went wrong when I transferred the database to the new server) - so I am closing the issue; thanks for your input