Striders standing on both on a small edge of a block and lava will not move at all, they will stay there until a player collides with them or lure
them with warped fungi. This doesn't always happen to naturally spawned ones.

To reproduce

1. While crouching, stand on a edge of a block
2. Summon a strider that is in the location you are in
3. Switch to spectator mode so that you and the strider don't collide, and switch back to creative
   → The strider does not move