The bug
When a strider spawns with a baby on its back, the baby and the strider already have saddles on their backs.
MC-176459
Baby striders can spawn with saddles
Resolved
Fixed
4
Finnian land
kingbdogz
Confirmed
Important
Mob spawning
20w13b, 20w15a
20w18a
Retrieved
I think that the baby striders had a zombified piglin as a rider that despawned.