That would be normal, when you change the orientation of your screen from landscape to portrait and will clear when you load the next page.I get it occasionally on a Samsung S10+ using their internet browser. I thought it has something to do with screen rotation I think as that's when it happens for me.
That happens me every single time. It's driving me insane.I've had that problem as well but not very often.
The one that pisses me off more is when you scroll to the bottom then try and hit the SMB link and it thinks you've hit the advert and takes you off site.