Help Wanted Custom Avatar Mask not working - no animation playing at all

Hi,

I'm struggling with the AvatarMask/Animation layer system and i don't fully understand, what I'm doing wrong here.
This is the situation:

• I have an animated mesh of a non-humanoid thing (a machine), which imports as generic rig and creates it's avatar from imported mesh
• We added some extra game objects to the hierarchy in prefab and duplicated/modified one of the animation clips that was imported. The clip itself plays back fine when scrubbing through it and all objects move as they are supposed to.
• We want to add this animation on an extra layer and use an animation mask, to make sure that this layer does not affect the looping general animation of the model
• as I have learned, you need to create a custom animation mask for that via code, which I did with this script: https://forum.unity.com/threads/how...ect-hierarchy-from-scene.574270/#post-4398478
  This worked fine, the mask contains all transforms
• I applied this mask to the new animation layer and added the edited animation clip to a state
• when entering playmode and triggering the animation, the clip plays back, but NO transform/rotation animation gets played back - the clip is working though, because i can see the active/inactive toggles of gameobjects, which is also animated in the clip

What we tried:

• Removing the layer mask: the clip plays back just fine then - so it contains valid animation(but I would really like to get the mask working)
• Creating a custom avatar for the animated model as well (via code) and added it to the animator (no change)

I don't get why it is not working. Can anyone help out here and give some guidance? Is it a bug?