Teams / Exchange Server OAuth broken for calendar delegation?

HI,
one of our customers has got the same issues in an Exchange hybrid enviroment after working fine for about half a year.

Some Exchange Online users can always use calendar delegation, some never can, despite having the correct permissions which were also recreated.

E.g. we have a delegator with 3 delagates, one is working fine all the time, two cannot schedule a teams meeting in behalf of the delegator.
Workaround doing this in owa for exo mailboxes works fine.

This started approx. on August 14th 2023, no changes were made on our side.

Also we have the same behavior with a stable working OAuth integration to onpremises, some delegations are still working, some not.

Since this week some random users which were working fine cannot delegate one day and the day after everything works fine again.

Atm we are circling around with microsoft unifying support, after some days of rereating the same permissions via exo powershell I will transfer again all Teams logs to support.