Bell icon notifications - old stuff at the top?

Hey fellow intranet experts!

Just noticed this morning that I have some really old read notifications (2-3 months old) hanging out in the top portion of my bell icon drop-down that have pushed down my most recent (couple hours ago) notifications down the list. Anyone else happen to have the same? 

Not a huge deal or anything, just curious as to why some older stuff is bubbling back up and taking the place of the most recent likes/comments.