Kryonoglou this discussion must have gone unnoticed sadly ?
The issue is the same content duplicating each time you open the notifications ?
This kind of "glitch" usually indicates a javascript issue happening inside the Mithril template of a component, causing issues with Mithril's diff algorithm and causing the same content to be rendered again and again.
I think I encountered it in the past, it could be caused by some posts containing strange markups and causing issues in the preview rendering, so possibly related to a third-party extension.
Could you check the browser console to see the javascript messages that might be there ? If there's no messages there it will be a bit complicated to troubleshoot further.