Ok, tested the current git version. The answers are back in the reply emails but in that reply emails the subject has now html entities in it (Ä ä Ö ö Ü ….) instead of the actual umlauts.
(when opening a new ticket - this email has the correct umlauts in the subject… only the replies made from ITFlow backend which were sent to the customer has the entities instead of the umlauts in the subject, in the text/answer itself everything is ok)
P.S.: Still testing and reporting bugs here (not in production use)…