It only happened to me and only happened once. The other players probably don’t have it enabled though, I have it on because I have been trying to learn how to make Add-ons, but the only thing that I had in global resources was a sound pack without any molang or player.json modifications. I have confirmed with the owner that no packs were on the realm itself.
The order of events that I remember was logging out to see if I could have my own resource packs separate from the realm, and enabling the tutorial sound pack from Microsoft Learn. After confirming that it worked, I left and disabled it, and later left again to do something else afk and it sat for about 5 minutes. I came back, saw that my own account was joinable in friends and was on the realm, but it showed 1 less player than my other friend who was on it, so I assumed it hadn’t updated yet and went to the home screen. Then this happened, I made a bug report because I’ve heard that there’s been a lot of problems in this update and this might help find the problems. There was also a crash at some point, but I don’t remember when and I have a pretty bad pc so I don’t know if it was a Minecraft problem or a pc bad problem.
It's actually showing half a heart less than you have, It's possible to have 0 hearts and not die because of this.
I don't know, it hasn't happened since that one time.