I was having a periodic issue where conversation view was not working on select emails. No clue why until now. Note, I only use gmail.
To fix it, after you've updated your inbox, go to your sent items folder. After you've updated your sent items, your inbox messages will be correctly grouped by subject.
To fix it, after you've updated your inbox, go to your sent items folder. After you've updated your sent items, your inbox messages will be correctly grouped by subject.