Anyone know what's going on here.. I put a magma slime in a boat, put it on a leash, tied it on a fence and know the boats invisable and magma slime stoped moving, I tryed to do it again with another magma slime it didint work, I play 1.13 xbox 360

Anyone know what's going on here.. I put a magma slime in a boat, put it on a leash, tied it on a fence and know the boats invisable and magma slime stoped moving, I tryed to do it again with another magma slime it didint work, I play 1.13 xbox 360