Adding new Animation to existing Animator not working correctly

I had to change my plans for my 2.5D Sidescroller from a Dash-attack to a simple Slash. Now I wanted to change the animation I had for the Dash to a new one I made for the Slash. I had to reimport my character and tried to move my Slash-animation to the Animator, swapped the Dash for it and tried it out.

My character consists of a stick-figure with a sword, done in Blender with an extra bone in the armature for the blade itself (imported as single fbx-file to Unity). For all Animations, that worked just fine, along with rotating the blade and everything. If I click the new animation in the asset-list and check how it plays in the Animator, it works just fine.

But! Once I try to use it inside the game, the blade doesn't rotate as it should anymore. it does still follow the hand, but no rotation whatsoever happens.

I allready tried to swap my existing model with the newly imported version... same issue.

Am I doing something wrong? Has the animation to be added in some specific way for the blade to work? After all, in Blender and in the Inspector, the animation works just perfectly.