I have had this problem happen three times so far. There is on instance that I am not even able to fix.
It is when it happened to this post:
When the post was first published on Schedule, only a fraction of what was on the latest edit mode appeared. The published post was a mess of formatting, and chopped up paragraphs. It published about 700 of the 1500+ words.
I went to edit mode to modify, add/delete, and nothing would show up in publish mode.
I reverted to earlier version and the one from the night before seemed to still have everything so I published that and it updated the post.
Few days later, I noticed that one paragraph is still a mess - in that 2 paragraphs got chopped into one. I went to edit the post and in Edit mode, either HTML or Visual, ONLY a fraction of the post shows up.
when I deactivated every plug-in, the problem still persisted, so I don't think it's plug-ins that are contributing to this.
To explain the problem clearly:
1. I bring up a post
2. The html editor shows all the content
3. The visual editor shows a chopped off version
4. I click back to the html editor, and it now reflects the (incorrect) chopped visual editor version
Then I disabled Thesis Theme and went to the default version, and the same exact problem persisted. I did this last step while all plugins remained disabled.
As a drastic step, I renamed my themes directory to themes-old (obviously this broke some things) but the problem above still persists.
I then reversed all actions above.
I look forward to your advice.