Using D365 online, nothing onpremp - the issue is when trying to track an email, you can search for an item to set the regarding to, but when you select it nothing happens, and the email is not being tracked. There is no error. There is also no option to track without regarding.
Sending an email directly from D365 does track the email.
This was working previously and just reported to me on Monday, and has been reported by multiple users. I have not made any recent changes so I'm not sure how it broke.
I've tested this an admin, and the issue is happening to the admin account as well - both on the desktop Outlook client, and the Outlook web client.
I have tried redeploying the Outlook app, testing and enabling the mailbox with no change.
I'm not sure what to try next, as there hasn't been any recent changes. I did also try rolling back the recent Windows Updated on a local computer, just in case, but that did not make a difference either.