Not sure what is happening, but since the 4.2.1 update and still with 4.2.2 update, after the app has been opened a while it stops responding to being able to drag and drop items into the Preview window or the Overview tree. When I attempt to drop something there is no indicator at all showing me where it will or can be dropped, and if I drop it anyways the page refreshes in the Preview window and the tree as well, and in the browser preview, but nothing gets added to the code nor the preview anywhere. I have to restart the program (maybe just project? haven't tried that yet, I will do that next time it happens) to reset it and then everything is fine again for a while.
I can't find any significant time frame, only that it's after it's been opened for a while. Has happened with 3 different projects so far so it doesn't look like it's project bound, and 1 of the projects was a 3.3.7 Bootstrap version and the other 2 were 4.1, so I'm guessing it's not a Bootstrap version thing. Not sure what else to tell you on it so please let me know if you need more information.
MacOS High Sierra version