Sprite Rigs get freezed in T-Pose after build or Editor restart

I don’t really know whats happening here:
I rigged a few Sprites with the ‘2D Animation’-package (Version 3.0.3) so I can animate them.
I gave them bones, geometry etc and it works perfectly fine.

The problem occures when I build the game or restart the Editor. Then I can’t move the bodyparts of my rig anymore and every sprite is in the T-pose.

To fix it I have to enter the sprite editor of a sprite, move a bone just a bit so I can press ‘Apply’. Then it is fixed for that particular sprite. Here a short video where I am showing it. This procedure has to be repeated for every single sprite.
I can’t even run the build of the game because it loads with the T-poses as well.

Is this a bug or did i miss something? I am using Unity Version 2019.3.0a10 and the LWRP Version 7.0.0

it is indeed a bug which is now on the public Issue Tracker (here)