Afraid I wasn’t able to make a screen recording, but on 2-3 occasions this morning, while on spotty Wi-Fi, we noticed a symptom whereby we’d written 2 lines of code in an app.js file, and all was well. We then added 2 more lines of code, but after a few seconds, those latter 2 lines suddenly disappeared from the editor. It seemed as though they were being echoed locally upon typing, but perhaps some save-to-server API call failed, at which point the error handler removed the new lines?
This seems like a different twist on session failure due to poor connectivity. In your case the session has persisted, losing data. In my case the session is usually silently broken, giving me the impression everything is working, then losing data later when I find I need to refresh the page.