Humanoid Avatar changes Pivot Point / Position /Pose on Play

Hey people!

I have a problem with animating Robot Kyle from Unity. I have to import him as a humanoid avatar to be able to use IK, but he behaves weird.
I import him as humanoid and everything works fine (he is after all an official asset, so I assume he's rigged correctly), BUT when I press play, he just bends his knees and slides down through the floor to his waist. The pivot point goes from his feet to his waist (his root node is there).
Here are the pictures: https://imgur.com/a/8c5G11D
So all in all his position changes, his pivot changes AND his pose. I have zero idea why.
I have seen other people having this problem, but I couldn't find an answer that applied to my situation. Can anybody help me? I've been stuck at this for days on end and I'm on a dead line and kinda desperate.

Thanks in advance!

Greetings,

CatTheGrimReaper

 

I -think- because the object is resetting to it's origin (0,0,0) - animation seems to do this, and I vaguely remember having this in the past and coming up with a solution.
What is Kyle doing in the scene?

 

@

Did you manage to solve this?