I am using the Divi theme, with it's built-in Builder feature. When editing a text box, the "Visual Editor" fails to load (this has the wysiwyg editor, etc.), and I can only edit raw text.
Checking all plugins, I have isolated it to Simple:Press. I'm on version 6.4.0.
Checking F12 in Chrome, and it reports multiple "DevTools failed to parse SourceMap" errors. Doesn't point me to any specific source, though.