All Admin Script Fields Are Blank After Update

I’ve been using this plugin for years — more than five years — and it had always worked well. Yesterday I updated it on all 6 of my sites, and every one of them showed the same bug. The scripts I was using are still there in the HTML, but all the fields in the admin area now appear blank and empty. I don’t even use a cache plugin on 2 of the sites, and the same error happens on all of them. It’s sad to have to abandon a plugin that used to work so well.