Root Motion acts differently in Animator Controller than in Import Preview

Hello :)

We have a strange problem: we use root motion for our enemy and created a side walk animation for it. When importing the animation everything looks great: Import is OK (click)

But if we use the animation in a blend tree, the enemy slides on the ground: Blend Tree is not OK (click)

We don't think that this is caused by an blending error of the root motion, because we set the blend values like this (since we already tried to use the animation in a "normal" state. This also doesn't work and the enemy slides on the ground):

So nothing should be blended at all...

Has anybody an idea what the problem could be?

Thanks for your help and have a nice day,

Severin