Microsoft Outlook Shared Calendar on iPhone not syncing

My wife and I have a shared Outlook calendar (set up by my account) which was working fine till this week. We could both add, edit and delete events on iPhone and iPad as well as windows laptop. Mine still work as before but her iPhone and iPad are not syncing. All entries are now being shown as created by me (even though some are not) and she is "invited" to them. She cannot edit or delete them. If I delete them or stop her sharing the whole calendar nothing changes on her iPhone and iPad. If she adds an entry on her iPhone it does not syncing to her iPad as it did before, nor on any of my devices (iPhone, iPad or laptop).

All devices are running latest software e.g. iOS 17.0.2