Microsoft 365 Business Premium shared mailbox not updating

[Cromulent]

I have four shared mailboxes and three of them sync perfectly but one of them doesn't sync at all. It shows this icon:

and I have no idea how to get it syncing again. It worked fine a couple of days ago so I'm not sure what is new as I haven't changed anything in the admin account for the tenant.

 

[visibleman]

Is it syncing correctly under OWA?
And i assume you manually attempted to sync the mailbox (ie - press the 'Sync' button)?

Edit - Just to add, if it's Outlook (Mac) then it seems to be linked to locally cached data (of the mailbox) and in the past either switching between legacy Outlook and back to 'New' Outlook (MS are removing legacy at some point though) and/or doing a 'Reset Account' on the mailbox seems to sort it. Sometimes it permanently fixes the issue for users, sometimes the user will have it happen again a weeks/months later.
Unlike Windows Outlook, there doesn't seem to be a way to permanently disable caching on (shared) mailboxes which is the 'official' solution there.

 

[Cromulent]

Is it syncing correctly under OWA?
And i assume you manually attempted to sync the mailbox (ie - press the 'Sync' button)?

Edit - Just add, if it's Outlook (Mac) then it seems to be linked local cached data and in the past either switching between legacy Outlook and back to 'New' Outlook (MS are removing legacy at some point though) and/or doing a 'Reset Account' on the mailbox seems to sort. Sometimes it permanently sorts it for a user, sometimes the user will see happen again weeks/months later.
Unlike Windows Outlook, there doesn't seem to be a way to permanently disable caching on (shared) mailboxes which is the 'official' solution there.

Thank you. Yes, this is macOS Outlook. I reset the account and that seems to have fixed things.