Admin / System - no

My system: Nextcloud 22, Ubuntu 18.04, Plesk 18.0.40
If i click on the admin site to System - there comes that error message.

The server was unable to complete your request.
If this happens again, please send the technical details below to the server administrator.
More details can be found in the server log.

How can i solve it?

In plesk i found in the log filte the following entry
Error 500 GET /index.php/settings/admin/serverinfo HTTP/1.1

btw - i saw my thread not - so i asked my question here twice, sorry.

there should be a error.log as well. serverinfo-app calls a lot of information from the system, that can trigger errors (should only happen when you open the admin-page).

i use ubuntu 18.04 - which error log do you mean?

It’s the webserver’s (nginx/apache) error log

In the apache error log is that standing, after i click in the nextcloud / admin / system:
[Sun Dec 19 13:01:34.641548 2021] [ssl:warn] [pid 21580:tid 139720537380608] (22)Invalid argument: AH02026: Failed to acquire SSL session cache lock
[Sun Dec 19 13:01:34.641618 2021] [ssl:warn] [pid 21580:tid 139720537380608] (22)Invalid argument: AH02027: Failed to release SSL session cache lock

If found the reason in thread of the plesk forum:

I resolved it by blanking the disable_functions item in the PHP setting of the domain from the website and domain menu.

Disable Functions - Gelöscht