Calendar not syncing with Outlook.com (invalid namespace meeting response)

I’ve noticed that eMclient is no longer syncing calendar entries from my Outlook.com (M365 Personal) calendar. eMclient version 10.4.5326 (97a2e75) on macOS 26.5.1 (25F80). I have both repaired the calendar and completely set it up from scratch. I always get the following error message:

[AirSync] Synchronization of the “[email protected]/Kalender” folder failed with the following error: Invalid namespace MeetingResponse:

Syncing with Apple Calendar and Outlook works perfectly; only emClient on macOS (2 computers) is affected by this, which currently makes it unusable for me.