Soulsand not slowing down player

[IceTank]

Soulsand is not slowing down the bot when using mineflayer.
I tested this on 1.16 with pathfinder and it did not slow down the bot at all.
When testing I also noticed a anticheat warning about flying. This might be a different Issue but it seams as if the bot does not sink into the soulsand block as a normal player would do.

[zardoy]

Soulsand is working but not when it has a slab or trapdoor above, it should also slow down the player when you're on that slab.