I suggest you use 'Developer tools' plugin to find the error instead of digging through the error log.

1 - Go to 'Plugins' page and activate 'Developer tools' plugin.

2 - Go to the plugin's settings page /admin/plugin_settings/developers

3 - Select 'Trace level' option and choose 'Log errors and warnings'

4 - Switch on 'Enable error log' option and 'Save' settings

5 - Now reproduce your critical error and check out log on the /admin/develop_tools/error_log page

Nikolai,  I can't go to the page because the error doesn't allow me to see the login page. However, if you tell me how to activate that plugin from the server side, I could edit it and maybe get results.

"Fatal error in exception handler. Check log for Exception at time 1751315922  " is all I see from the browser side".
Thank You.

This error was fixed by Optimizing Tables on the website's database. Also, it happened because o high use of memory.
Thank You.