I had the same problem. I found a fix but it was so specific to my specific setup that I can’t imagine it being the root cause.. but perhaps a symptom?
I found an error in my console for a missing JS file which traced back to a plugin, “Scissors for 2.9” — I disabled the plugin and tracked down what I can only guess is its replacement: https://www.ads-software.com/extend/plugins/scissors-continued (great cropping utility, btw). I installed and activated the new plugin and it works great. I noticed some other quirks w/ the new 3.1.3 update, so maybe there’s something deeper conflicting with plugin architectures.
Best of luck,
Dustin
