I’ve been having notifications come through months late recently. For instance, this user tagged me in their observation in June, but I just got the notice today. There have been a couple other instances of this as well recently.
sometimes I edit an existing comment - a new @ tag on an old comment will cause a new notification
I discovered recently that bulk-edits can cause this too. A user bulk edited some pin locations and it caused a small flurry of re-sent alerts.