When summoning a shulker of scale 0.5, you can see using F3+B that the first tick's hitbox is off-center, causing you to get pushed out. It's always aligned so it touches the block's north-western corner, so the displacement gets more extreme the smaller it is.

How to reproduce:

1. Execute the following commands:

   /tick freeze
   /execute summon shulker run attribute @s minecraft:scale base set 0.5

2. Press F3+B.

Expected result:

The shulker's hitbox would be immediately centered.

Observed result:

The shulker's hitbox is not centered for one tick.