Hi @Joshua Modine ,
According to your description, does this issue only happen to several specific users in your organization or happen to all the users? If only happen to several users in your organization, please try to compare the differences between those problematic users and normal user to see if we could find some clues (such as Outlook versions, access permissions to the room mailbox and so on).
In order to further confirm your issue, it is suggested for you to try the Scheduling Assistant feature from Outlook web mail to see if the same issue can also be reproduced there.
If everything can work fine on your web mail, looks like something might be wrong with your Outlook desk top client. Please make sure you have fully updated and repaired your Outlook desktop client.
If the same issue could be reproduced on your web mail, I'm afraid that issues might be more related to those problematic email account themselves. It is more suggested for you to check if there is any corruption within theses email accounts during the migration.
Any update about this issue, please feel free to let me know.
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