However, the first step with troubleshooting is to rule out third party code and modifications by disabling all add-ons and reverting to a completely default unedited style, with all custom JavaScript (including ads) removed.
I have turned off all my plugins but still facing the same issue,
I performed this test:
1: paste in three paragraphs.
2. save post.
3 edit post, remove third paragraph.
4. save post.
5. edit post: You will see the third paragraph you removed is now back again in the editor.
6. press save: The third paragraph has now been edited back.
I made a new thread with 3 paragraphs.
I then edited post and deleted one paragraph.
Saved Edit.
the post showed only 2 paragraphs.
I then went back into edit and the edit showed 3 paragraphs.
Without changing anything I left the edit and went to the main forum.
I then went back into the forum and my new thread did not show until I pressed refresh on my browser.
My Server uses a software called XVarnish, Apparently it caches your site to improve speed times, I have turned it off and the problem seems to have gone away.