My pc, maybe because of the external keyboard I'm using, occasionally decides that Scroll Lock is On and then Excel becomes unusable ... The solution is to bring up the On Screen Keyboard and toggle the virtual scroll lock key ...
I wonder how that happens? Do you press Ctrl-Home a lot (to go to the very start of a document), and maybe you missed and hit Fn-Home, if you have a Dell OEM keyboard https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F... , Fn-Home toggles Scroll Lock...
Yeah I suspect its something like that. Its been hard to track down because its only noticable once you fire excel up