In the nether, minecart with a player in arrives at unpowered powered rails ending in an andesite block. If the player pushes forward while still in the cart it drops into a space below the andesite block but there is solid netherack in that space. The player starts taking damage. If the player exits the cart it is sunk into the netherack floor. Removing the unpowered rail and replacing it temporarily fixes the issue but if the player returns the bug is reintroduced.