Hi ntozier,
I got feedback from the server admin: In the php_error.log we were getting the following warning:
[25-Jan-2022 08:20:50 UTC] PHP Warning: preg_replace_callback(): Allocation of JIT memory failed, PCRE JIT will be disabled. This is likely caused by security restrictions. Either grant PHP permission to allocate executable memory, or set pcre.jit=0 in /opt/osticket/upload/include/class.orm.php on line 3450
After setting pcre.jit=0 in the php.ini and restarting the error is gone but the problem with editing the template persists.
Seb