I haven't seen any other threads on this, but so far I have gotten 3 of these notifications, I have an indication of a notification, but when I click to check there's nothing there. There's also nothing in messages.
I'm not certain, but the only thing I can think of is it has something to do with pings! For one of these notifications, I remember seeing someone ping me with all the spelling and capitalization correct, but I didn't get a notification, and got one of these ghost notifs 30 minutes later. I haven't been able to find any pings for anything else though.
I use google chrome on deskptop.
