I know this is an older post, but I was having the same problem and think I figured out what the issue was. At the top of my Inbox, to the right of where it says “Manage notifications,” there are three dots (More actions). I clicked that, and then clicked “Expand notifications, Show more context.” The tasks on the left side of my inbox expanded to show additional notifications, including places where I had been mentioned. I hope this helps someone else, it’s been bugging me for awhile!