Noticed this a while ago and just saw it again:
The purple banner at the bottom of the forum page extends further than the normal container does, causing weird scrolling behavior.
Maybe something that can be fixed soon? 
I think I made it work better. Let me know if you still experience this. Thanks for sending this our way.
Hi Charlie,
Still experiencing this bug. I noticed, this just seem to happen as long as I am logged in.
What phone and browser are you using?
iPhone 14 Pro, iOS 18.1 using Safari