Facebook scrolling in iPad

My iPad Pro suddenly started to scroll uncontrollably in Facebook.com tonight. When I load FB in Safari it looks OK until I touch the screen and then it starts to scroll. It doesn’t do it in any other Safari page and it doesn’t do it in the FB app. AFAIK I haven’t done anything to initiate this. I have restarted the iPad several times without any difference. I was on iPadOS 14, so I loaded up the new iPadOS 15 but that hasn’t solved the problem either.

Any ideas?

[Re-Titled by Moderator]