Appointment series: Participants are damaged or username@z-push-hostname participant is added when element is edited

[segro]

Hello all,
Client: Office365 with kopano plugin
server: debian10,kopano 7.2 z-push 2.6.2

If an element of a series of appointments is edited as described above, e.g. with the agenda, the participants behave strangely.
Often a participant is added, namely the editor as username@z-push-hostname, which of course cannot be delivered.
Sometimes participants disappear or even both.

Are there any solutions to this?