XF 1.3 Uncaught TypeError after migration


I have transferred my XenForo from one server to another using Plesk Migrator. Many features work as expected, however creating conversations does not work. I am able to create them, however, I am then unable to open them. This is the error message from the logs:
PHP Fatal error: Uncaught TypeError: Argument 1 passed to XenForo_Application::handleException() must be an instance of Exception, instance of TypeError given in /var/www/vhosts/server.com/httpdocs/board/library/XenForo/Application.ph> mod_fcgid: stderr: Stack trace:, referer: server.de mod_fcgid: stderr: #0 [internal function]: XenForo_Application::handleException(), referer: domain mod_fcgid: stderr: #1 {main}, referer: server.com mod_fcgid: stderr: thrown in /var/www/vhosts/server.com/httpdocs/board/library/XenForo/Application.php on line 361, referer: server.com

The old server is still on production. Maybe this can be the problem? The new server tries to access some domains which are still pointing to the old server which is rejects the request?

Can anyone please help me?

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