To explain this issue in a bit more detail i need to give some context.

The world this issue was discovered on was on a server hosted by a 3rd-party server provider.

Many hours into gameplay i decided to move far away from spawn, and travelled to around -4000Z in the nether and found a village to setup a base in.

After many hours of gameplay i managed to create a cartographers table, and even get a Villager with the Cartographer profession.

When leveling this Villager to Journeyman, something went wrong, and the world had a massive lag spike. After this, everything seemed like normal, and i was now able to trade for a Woodlands Explorers Map.

After purchasing the map i decided to travel to the nether to gather some ore, however, when entering the game was loading much longer than usual, and when it finished everything i had dug out in the nether was gone. Travelling back to the Overworld was to a bigger shock; The village had reset, and all my items were gone.

After looking in the server console i noticed the error messages provided in the first photo below.
Loading a Vanilla server on my own computer did not cause this exact issue, but it caused major lag spikes (see picture).

I am yet to try to reproduce this issue on fresh Singleplayer worlds, but this could be a major bug with cartographers, or maps in general. If a server auto-saves at the wrong time then this could possibly risk a loss of all world data.

The world-file where i have managed to find this issue can be found here.
NOTE! It's over half a gigabyte!
I have a save of the world before the issue occurs, and i am able to re-produce it by following these steps:

1. Trade with the Cartographer to make him level up to Journeyman (seems to take 1 trade)
2. Wait until the lag spike finishes
3. Trade with the Villager for the map
4. Put the map in an item frame, close to the other map in the house (see second picture)
5. Travel to the nether

I have not been able to fully re-create the issue in Singleplayer, as force-crashing the game after entering the nether seems to fully load the chunks, so this might be a server-side only issue. Hopefully this will help with finding the root of the issue.
NOTE: In case loading the world in Singeplayer/Multiplayer with a different account, the co-ordinates for the village in question is X=-747, Y=65, Z=-32140