When a shulker is uncomfortable (eg, end rod pistoned into its head) it will not teleport to a location either directly next to or on a direct diagonal to another shulker.

Screenhots show example of mob switch that worked prior to 1.14.3. It has two chambers where shulkers stay until pistons extend and put end rods into the shulkers head. Shots of each chamber show shulkers with end rods in their heads not teleporting to valid positions in the second chamber as they would be in a 3x3 area centered on another shulker.