Oct 26 07:41:20 lda(peter.nabbefeld@gmx.de)<24607><UvPzGACp0lsfYAAA7IIYzw>: Panic: file istream-crlf.c: line 24 (i_stream_crlf_read_common): assertion failed: (ret != -2)

$ dovecot -n
# 2.3.3 (dcead646b): /etc/dovecot/dovecot.conf

Are you using our packages from https://repo.dovecot.org/? If so, it would be helpful if you could send the core dump to us (e.g. email privately to me). As for getting core dumps, see: https://dovecot.org/bugreport.html#coredumps