I'm kiting a wither skeleton to the end city to finish off How Did We Get Here. My end portal leads to a small room in the middle of a bunch of end stone. I quickly realized that I had only carved out a passage up two high, and he was stuck. So I cleared it and he followed me up the stairs, until he got here:
He's shaking and shimmying and not moving at all. I've widened it out, and there's nothing above him.
Second picture, I went down and back up, cleared out a lot around him, and got him up a couple steps, and he sticks again.