Raid mobs originally were intended to spawn within loaded chunks, but now that simulation distance is added, raid mobs can spawn outside it and just remain frozen, never approaching the village until you move towards them. This can slow down raids significantly, especially if you have a high render distance and a low simulation distance.

Tp reproduce:

1. Turn simulation distance down to 5 (while having a higher render distance)
2. Turn entity distance up to at least 150%
3. Find a village
4. Start a raid
5. Move to one side of the village, just within the area where the raid bar appears
6. Wait for a raid wave to spawn outside the simulation distance. If a raid wave doesn't spawn outside of simulation distance, use the following command: 

   /kill @e[type=#raiders] 

7. Observe that raid mobs will spawn outside of your simulation distance, remaining frozen forever until you approach