Downscaled mobs can phase through walls and suffocate upon chunk reload

Entities have a “scale” attribute that changes their size. When a chunk is reloaded, entities with a sufficiently lowered scale may take small suffocation damages, if they were standing next to a wall. Given sufficient unloads and reloads of its chunk, the entity may eventually die.

Repro:

1. Create a small enclosure, walled with full blocks. (See screenshots).

2. Spawn a chicken in the enclosure.

3. Reduce the chicken’s scale using the command: /attribute @n[type=!player] scale base set 0.7

4. Push the chicken against the wall.

5. Exit and re-enter the world several times.

6. After each reload, check the chicken’s heath using /data get entity @n[type=!player] Health. The chicken loses 1HP every reload, and eventually dies.

Additional Informations:

A simple walled enclosure is enough for the entity to potentially suffocate, but only if the entity’s scale is low enough. Here the chicken must have at most 0.7 of scale. It will only ever take one tick of damage after every chunk reload. This behaviour is close to what I observe while playing in a world with randomized mob sizes, where my farm animals end up spontaneously dying.

In the attached screenshot, I also put a small contraption that uses water to push the chicken against the wall. In this scenario, even a scale of 0.99 is low enough to cause the chicken to completely phase through the wall, and immediately suffocate to death.

For some reason, baby animals appear to be completely immune to this issue.