I wasted a loooong time trawling websites looking for answer to this, as the same issue was driving me nuts! The solution was so simple that I'm still slapping my head at how obvious it was!
Anyway, for anyone still struggling with it, here is the solution: just UPDATE OUTLOOK!
Apparently this was a known issue and they fixed it in an update, but nobody on any of these pc advice websites knew about it. On Outlook, click 'help' at the top and then follow whatever steps it tells you to take to get it updated. You're welcome