Physics objects sometimes stick to each other

Hey everybody.
I am working on a stacking game in “2D Side Scroller” Mode and I spawn boxes at my anchor point. Now my problem with the boxes is, that they sometimes start sticking to each other which is not great for a stacking game. The boxes are from the parent class Actor and have a collision box generated by the engine when importing the paper 2d sprites. I hope somebody can point me into the right direction to let them behave like normal objects that collide and stack but do not stick.

If you need more infos / screenshots of objects let me know.

Thanks in advance for your time, very appreciated