I’ve had this problem off and on for a few months on both iPad and iPhone, where for my work M365 account, this error keeps popping up.
Turning the calendar off and on in settings will clear the error, until the next time.
Anyone have ideas on a more reliable fix?
An answer here suggests turning off calendar sync, clearing, and resyncing, but also suggests not using mobile for accepting invites!
Indeed, this is also echoed by Stanford to students: