Had to duplicate this as it was a week old and got no responses.
Steps:
Spawn a shulker
Then, spawn a warden on top.
After this, if you can get it to target another shulker, it's pathfinding will glitch and will make it spin or continously headshake.
Please do not create duplicates of your own reports, even if they have not received a response for a long time. MC-255549