Vindicators do not despawn when player unloads them

I was playing in the latest MCBE version when I noticed a pillager patrol had spawned. It was getting night so I went back to my base to sleep. When I came back I noticed every other mob from the patrol (and ones that had spawned due to low light levels) had despawned because I had moved far enough away. I have made a short unlisted YouTube video here. The world I show this on is on the latest release (1.16.221) and the world had a simulation distance of 4.

Video of this happening: https://youtu.be/87omTJASvlM
I dont think this happens with every vindicator, therefore I am not sure how to re-produce, it could be because mobs aren't meant to despawn in raids and it thinks its in a raid?

This is not a duplicate of https://bugs.mojang.com/browse/MCPE-75470 because it spawned when it was meant to, just didn't despawn.