I seem to have found a fix for this, at least for anyone else using C3 r204.2 on Android with Chrome. I can't imagine how many crazy things I must have tried to restore C3 when this would happen, and that's why I'm actually a little disappointed with myself that I didn't figure this out sooner. All you have to do is tap the back button (<) on your phone until you get a dialog from construct asking if you wish to "leave" or "stay". Tap "stay" and you'll be returned to the editor with everything working properly.
This has worked consistently for me on Android. Hopefully a similar procedure will work on desktop as well.
A couple more "clues" I've observed, don't know if it will help though. When the editor is greyed out I am still able to swipe left and right to scroll through the various bars. The bars are unresponsive and greyed out also, but if I tap and hold on an item in the bar I get a vibration, but nothing happens.
I hope you guys fix this soon. I've had to redo a lot of work because of this, but at least now it's just an annoyance. My mechanic hates intermittent problems too!