The mentioning thing happened over a few days, so I have logged in and out regularly. I always clear my cookies before I turn off my laptop. Anyway, thanks for the suggestions.
I got your mention. The mentions I didn't get were from Evil UU (only person who mentioned me in those few days, so I don't know if it's because of his account or not), and they still do not appear in the 'Mentions' tab of my profile.