IDK why this bug is not detected throughout almost 7 ~ 5 years or more, and I hope we get any fix soon about this…
In a nutshell, SOMEHOW All of these paper2d components are not be handled with depenetration system in physics engine.
Example video for my explaination.
https:///
(I forgot to release the movement constraint of all objects at xz surface, but I tested without the constraint and the result was same)
Depenetration is a sort of method that physics engine use to adjust the transforms of the overlapped objects by checking the depth of penetration and repel those object from each other.
This is very important logic when it comes to collision detection, because even we immersively detect the collision of a physics body continuesly, It must have some unexpected gap between last frame and it can go wrong easily and often. We can not prevent physics bodies from overlapping each other clearly.
Depenetration is the problem solver in this case. When the engine detect something went wrong in physics, they try to fix this problem by making those bodies ignore colliding each other and repel each other.
And somehow, It seems that this beautiful system is not implemented (or does not affect) paper 2d components.
As you can see in the video, This is why it once get stuck each other than it never be seperated automatically, unlike other objects. They repel each other when they started to be overlapped. (like static mesh component)