for some helpful config, the below is the logging config I have and logs have never been an issue.
You can even add 'logfile' => '/some/location/nextcloud.log',
to get the logs in a different place
'logtimezone' => 'UTC',
'logdateformat' => 'Y-m-d H:i:s',
'loglevel' => 2,
'log_rotate_size' => 52428800,