Most mobs (Skeletons are the only exception as far as I know) are unable to pathfind on and/or to carpets with torches underneath.

To reproduce:

1. Make a floor out of any block you can places torches on (Stone for example)
2. Place torches on top of the stone
3. Place carpets on top of the torches
4. Spawn a few mobs on the carpets

Here's a video on Streamable showcasing the bug: https://streamable.com/s7qidg

Possibly related to MC-96319