Topbar weird behavior when bottom scroll

I've been having this visual problem with the topbar for a while now, especially when I scroll down. It's probably due to my setup, I don't really know, has anyone had this problem before?
Thanks !

Edit1:
In fact I think it's related to the topbar, but just that the sidebar scrolls with the main container or its display pages, I'm having trouble grasping, I'm on a fresh install