Just a small update. I did find another page just recently that had the same problem (blank on the Frontend and Editor). The page had not been edited for 3 months. This is a very rarely used page so I haven’t checked it probably since the last edit. Anyways it also had an emoji in the content as well.
I went through the same process as last time to fix it. It worked and I also added back in the emoji.
Anyways since this happened to me on more than 1 page that means it was not a one off saving issue.