Size volumes don’t seem to change the size of clients if potions permissions are disabled. Even if the player inside has their own special items use permissions, they won’t change the player’s size. They will change the host’s size just fine.
Summary of bug here.
Steps to Reproduce
Place size volume with changed size (In my case i had it set to 1.3)
Turn off potions permissions
Clients joined will not change size.
What I expected to happen
For volume to change other player’s sizes
What happened
Size of other player’s doesn’t change, unless potion permissions are enabled.