Recurring meetings don't work anymore (new issue 1 of 2)

My spouse has sent recurring meetings from her external work account (using Outlook), which display correctly in my external work account (with a different organisation, also using Outlook), but not in my mailbox.org account (either in Webmail or the Android calendar app, which is synced with DAVx5). In my mailbox.org calendar, only the first instance of the meeting shows up, but none of the repeats.

The email with the calendar invitation already displays incorrectly as just a single, non-recurring meeting.

This seems to be a new problem that has come up in the past couple of weeks - recurring meetings worked before. The issue does not exist in the other direction: I can send a recurring meeting invite from my mailbox.org account to my external work account and my spouse's external work account, and they recognize it as recurring.