This is an unusual situation. I suspect your very long pages might be the reason for your problem. That is a somewhat unusual way of building pages.
The only suggestion I can think of is to try and change your theme to a different one and see if the problem persists. If the problem is gone, before you get back to your original theme, remove half of your content and place it in a new temporary page. Then switch back to your original theme and see if you can scroll in Edit Mode. Good luck…
BTW, make sure that all your addons are up-to-date (themes, plugins, Stacks and stacks).