Sorry for bumping a very old thread, but revisiting this issue now that I've upgraded to the latest version and still having the issue.
Tested on the default, unaltered theme and still having the same issue there as well as our third-party theme. I notice a similar 404 error as listed above when i try to drag and drop modules on the home page as well, with them not working, looking at the console and it's giving that same 404 error for that .js file