Hi @Steve Payne ,
Is there any error message when users fail to check the free/busy information in the other databases?
Any relevant logs in the Event Viewer?
How about moving one of the users' mailbox from the newly created database to any one of the old databases?
Besides, it's suggested to try moving the newly created database to the other mailbox server and see how it goes:
Move-ActiveMailboxDatabase <newdb> -ActivateOnServer <servername>
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