Riding entities that cross chunk borders will detach from the rider after reloading

Partner Rank:
2

Summary:

An entity positioned on the edge of the chunk that has seats that are positioned within an adjacent chunk will result in any entity riding in those seats being evicted after the game reloads.

Verification builds and Platforms: 1.18.2.03_RC2 - R18 RC 

Impact:

Entities riding another entity will no longer be riding the main entity. The rider on the next seat will fill empty seats changing the order of riders. This results in the entity becoming broken. This can lead to player confusion and map issues for an unseen reason (chunk borders are hidden) 

 

Repro Steps:

1. Download and play the test world on 1.18.2.03_RC2 release.
2. Open the world and call a function: “/function test” 
3. Notice that red concrete represents the edge of the chunk
4. Optionally press F3+M to activate chunk borders 

1. Reload the map.
2. Notice how the summoned test entities on the red concrete “lost” some of the riders. “Lost” ones are just no longer riding so when the seat is empty, the entity in the second seat will move to the first seat.
3. Reload the map again.
4. The same thing will happen again. One seat will lose the rider, next rider will come to the empty seat.
5. Try placing the test entity using its spawn egg from your inventory. 
6. Reload the map.
7. Similar outcome will happen to any test entity placed on the red concrete, but any placed on the white concrete will be fine.

Observed Results:

Entities riding near chunk borders are detached from the main entity when the world is reloaded. The entities that remained on seats will move down to empty seats.

 

Expected Results:

All riding entities remain in their seats the whole time, regardless of position within the chunk

 

Regression Builds:

1.16.200, the introduction of the /ride command

 

Notes: Contact Greg Walls on Slack for the world to test.

Tested with villagers and custom entities, and the same issue happened. This uses the /ride command 

It is similar to [MCM-671https://bugs.mojang.com/browse/MCM-671] but has a different observed outcome