Sam I just had another thought about your problem, it could be that there's a conflict between Outlook and one of your extensions.

Click onto the 3 dots and then click onto Extensions and then Manage Extensions.

Turn off one extension and then check out Outlook to see if you're still having the problem, if you still have the problem than turn that extension back on and turn off the next extension and repeat the procedure.

Do that with each extension. If turning off one of your extensions fixes your problem, then leave it off.