Ehm… I have this very weird behaviour lately… It would be hard to describe so here is a video:
https://drive.google.com/open?id=1PbvR4geRkIsCQh5JExH4kryTVC0oDcJ0
I thinks its not related to any of your updates I think its related to browsers updates… I am using the very last Chrome version (62.0.3202.94) although it was happening on a previous one and it happening on the latest firefox as well. :-O On ALL my websites! (currently 4 websites running on JA Builder).
It started like 10 days ago I think and it only happens on Advanced tab of blocks with a lot of informations in this tab.