Cave Spider Spawners in Mineshaft appear to be missing spiders

I upgraded an established world to caves and cliffs experimental mode and flew outside of the explored chunk area.  I found a large abandoned mine shaft.  I found 3 spawning cages but they didn't have the cave spiders inside spinning around or on fire to indicate they were active.  I didn't see any cave spiders spawn out of them.  

Seed is -875330636.

 

steps to produce: 

1 create world in 1.17.10

2 convert world to an experimental copy

3 go to the mineshaft around -1400, 14, 500 and find spawners with no spiders in them.