I was playing on a new Realm: Java Edition(one which I do not own, but I know the owner) which was newly started for the 1.19 update. This time we set the realm to creative mode. After a couple hours of game play, the owner logged out. I stayed on and played a little while longer. Then I logged out. about an hour later I logged in again. All progress was gone pasted 1.50. So later, I started over. I rebuilt the progress that I had lost. I kept logging in and out periodically to make sure it was saving. I got the owner involved. They logged in and out at various intervals, working on our builds. It appeared the realm was saving our progress. We kept building.
     The next morning, out of curiosity, I checked. All our progress was lost, both mine and the owner's. The world seems to be stuck at a TIME PLAYED 1.50 on the statistics page. The realm continues to reset back to that time somewhere between a half hour to an hour of inactivity or game play.
     As a side note, I believe it is also happening on stand single player/lan based worlds according to a friend of mine. He has tried redownloading the game. progress does not save. I do not have the environment or further details for what he is experiencing.

I hope this information helps because we love playing Minecraft!

Thank you!