I was going to submit that it would be great if on drag and drop it could be transparent as you can't see the folder you are dragging to. I switched to Chrome "to just see" and it is transparent. This means it is there and a complete browser inconsistency. I have also tested in Firefox and it works so know this is truly a bug too be fixed.
Looking at the differences:
- Edge shows the message in a giant blue box
- Chrome/Firefox show the message as an email icon (transparent)