Check out this video for some evidence of the problem…This one doesn’t even involve HTML, just wordpress not saving. We typed in a sentence, saved fine, then made a change, hit save, and it reverts back to the original.
https://screencast.com/t/LegofdI9A
Still totally stumped here. The problem seems random too, sometimes it will take, sometimes not. Most of the time, not. And the longer or more complex, code-wise, the story gets, the less likely it will save.