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Hi ​@Marc Mazurkiewicz 

Sadly, I can’t help. If I were faced with this I’d probably try an incognito window (to rule out any kind of plug-in or extension issues). Try dragging and dropping something you know will work, like a website. And then checking the so-called “debugging console” of your browser. This is getting into the direction of development, but browsers like Chrome and Safari give you tools to “look under the carpet” and see what is really happening.

Reason: dragging and dropping (under the carpet) is amazing complicated, depending on what you are dragging and dropping, where (you say a web app which narrows it). 

If you are a licensed user with a support model, probably a good time to raise a ticket.  “Was working but now it’s broken” is probably a nice thing, in terms of getting a fix!

GOOD LUCK!  Ken