Sometimes piglins will freeze in place instead of running from things they're afraid of (soul fire items and zombified piglins). When a piglin spawns in near some zombified piglins, it will run away for a second and then stop and freeze in place. When it does this, you can place soul fire items near it, and it won't run away until the zombified piglins have moved far enough away from it.

https://www.youtube.com/watch?v=_9mINNlIPmw

In the video, when the piglin is frozen in place, it seems to make the "piglin retreats" noises. Piglins also unfreeze after reloading and after being punched.

I've also seen this happen to piglins that have already spawned in, but I haven't been able to figure out what circumstances make that happen.

I have managed to find a pretty quick way to reproduce this bug. This is a creative world, the seed I'm using is 152924862, the simulation distance is 4, and the render distance is 20.

Steps to reproduce:
1. Be in a Nether Wastes or Crimson Forest biome
2. Spawn in some Zombified Piglins and place soul fire items around the area liberally
3. Fly around the area to allow Piglins to naturally spawn near the Zombified Piglins (some will run away and behave as expected)
4. Eventually, a piglin will spawn in, run a little, and then freeze in place
5. Place some soul fire items near it, and it won't run away

Expected Results:
The piglin will always run away from things it's afraid of.

Observed Results:
The piglin freezes and does not run away from things it's afraid of until the zombified piglins move far enough away, or until the player interacts with the piglin in certain ways. (I have not tested to find all the actions that are able to snap a piglin out of this frozen state)