So I was building on my creative world, then I got an error message minecraft "run out of memory". I relaunched the game and started again to build on the world. Maybe 1 day after this I noticed that some of the changes that I made before that error message were gone and some changes that I made after were still here. Now I noticed that in an specific area the changes that I make are saved but in most of the map all the changes that I make are not saved. I thought that the issue was linked to the error message that I got before but the day I had the error message I "upgraded" my world from 1.15.2 to 1.16.1 (just before in the morning), so I dont know if the cause of this bug is one of these 2 reasons or maybe something else.

If smomeone has an idea please help me