I did find one small bug while playing: if you drag a letter off the grid, it doesn't properly update the squares on the grid for that group. The space where you removed the letter stays blank, and the remaining places don't show the recently removed letter as a possibility. I noticed that it works as expected when right-clicking to remove the letter, however.
I couldn't reproduce the bug on three different browsers, so there's probably some kind of an additional constraint for just what triggers the bug. Based on the description there should be an exception printed in the the JS console. If this happens again, I'd appreciate seeing the top of the stacktrace.
(And in the meanwhile, this is is an object lesson that exception reporting to the server has to be included even in an MVP. Anything that one player reports, dozens of others must have seen and not reported.)
I'm using Firefox on Linux which could very well be the culprit here -- I recall an issue with drag and drop that was fixed in a recent changelog. I'll reach out if I run into the issue again.