I already found the problem. I have php errors:
PHP Fatal error: Allowed memory size of 1073741824 bytes exhausted (tried to allocate 262144 bytes) in /var/www/html/include/class.orm.php on line 417
PHP Fatal error: Allowed memory size of 17179869184 bytes exhausted (tried to allocate 20480 bytes) in /var/www/html/include/class.filter_action.php on line 243
That leads to not delete email and a re-imported ticket.
The memory is not the problem, I tried with 64GB. I think there is an infinite loop or something.
A workaround for me was to disable all filter actions with reply-to.