I have been playing on a world for a couple of months now. All of the sudden, I've found that the world now reverts to the original world state whenever I save and exit. The only things I retain are my current inventory, toolbar, advancements, statistics, current location, and levels.

I have no idea why this is happening, though it appears to be similar to MCPE-42226 from the Bedrock edition.

Judging by the report linked and the save files below, steps to reproduce might include:

1. Start a save
2. Travel throughout the world to increase save size (files approximately add up to 164 MB, so attempt to get to that)
3. Build something and keep items in your inventory
4. Save and quit to title