Shulkers will teleport if there is another shulker next to them even diagonally
How to reproduce:
1) in a 3x3, spawn shulkers on the edges (purple concrete)
2) spawn another shulker in the center (red concrete)
1 or all the shulker will teleport, it also happened that the central shulker teleported instantly upon spawning
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Sounds like MC-183884