Mesh deform on bone rotation

This case is giving me a headache. So I’ve made sliding doors (opens to both sides) and there should be a moving lock on one of the sides and when I rotate the bone (vertex group assigned with 100% weight) it scales down the mesh to almost 0% when on 180 degrees rotation. I know that to fix this I should use “Preserve Volume” on armature modifier, BUT I need this to be exportable to Unreal Engine 4 (Preserve Volume doesn’t work in UE).

And now I don’t know what I did but it does not deform anymore (without Preserve Volume). I’ve looked through OLD and NEW saves looking for changes but couldn’t find any.

Bones “LockBase” and “LockTier1” control the lock anims.

If anyone experienced with this could help me so I wouldn’t make same mistake again I would really appreciate.

Attaching both broken and working blend files ins zip file (couldn’t upload broken one alone Oo). (967 KB)