I am not able to scroll my retool app in preview mode. When I go to edit mode, it is working fine
Is there any chance your app is fully contained in the app header frame? If so, moving some of the larger components (or all of the components) down to the main frame should resolve this 
Another option could be to toggle off "Fixed position when scrolling" in the header frame settings
This does appear to be a recent behavior change, so I'm also requesting a fix from our engineering team. I'll post on this thread with any updates