Exchange Hybrid: Only On Prem shared Mailboxes noch updating

Hi, we have since about 8 Weeks the problem with several customers that users whose mailboxes were stored on O365 can no longer cache the contents of OnPrem mailboxes. If I disable caching for the shared mailboxes, everything works as before. We have tried several things, but until now no solution was found. Is this a known bug or any workaround known?

regards

Armin