I would assume this is related to Refresh 2 bringing in Form builder section properties and the rich text editor being made available, Kentico would have altered JS (and maybe other assets) to get the updated functionality working.
It is worth noting that you should be clearing your browser cache after each hotfix, as per documentation recommendations:
All users who work with the Xperience administration interface should clear the cache in their browsers after applying the hotfix. Otherwise, some features in the administration interface may not be displayed correctly.