I don't check my messages anymore and lately instead of going up, the number of messages has been going down (I think it was near 9400 a few weeks ago, now its at about 9000). I know this is mostly on me for being lazy and going months without checking my messages, and that its probably just server lag or something.. but does anyone know why exactly this might be happening?

My browser / operating system: Windows NT 10.0, Chrome 118.0.0.0, No Flash version detected

if your notifications are composed of mainly comments, then it might be that some of the comments have been deleted.
Infact, just tried with main:
(commented)
(deleted)

Comments could've been deleted