Witches, for some strange reason, are put in a slightly higher position when in Minecarts than other mobs. This could possibly end up causing suffocation.
How to replicate:
Put a Minecart on a rail, then put a block 2 blocks above the rail, so that the Minecart has a 1 block space above it.
Place a Villager in the Minecart, and observe that it dosen’t sit down, but also dosen’t suffocate.
Cancel the Villager’s subscription to life
Put a Witch in the same Minecart
Expected result:
Because Witches and Villagers have identical hitbox height, if the Villager can stand in the Minecart without suffocating, then the Witch should too.
Actual result:
The Witch suffocates.
Please confirm if this is still an issue for you