hmpf

probably related to MC-200906

I can confirm the incorrect player-detector behavior.

The title is misleading though, because the hitbox is actually rendered correctly (F3+b) both before and after loading the world (or chunk).

I have attached a few images showing the construction of such a detector, as well as the state before and after world/chunk reload.

As you can see, the hitbox of the fish is exactly the same in both cases, yet the pressure plate is triggered.

Edit: this is likely related to MC-149495