Edited reimported fbx meshed up animation root

I’ve downloaded a model from the Asset Store but since I needed to edit some stuff (UV mapping as well as animations) I took the fbx file and imported it into 3DS Max. After doing all the editing I had in mind I exported the model and re-imported it into Unity. But then I realized something strange regarding the animation that were already present inside the unitypackage.

As soon as I pressed play the model would jump down so that the model’s middle is in the 0,0,0 position. I tried tweaking the model changing the Root Node to the Spine, but this seems like a workaround and it only “kind of” improves the situation. Although the model does stay in position during animation it now seems like its feet are on the air. Don’t know how to describe it better, but it seems like it is hung by a thread attached to its spine.

I suppose there’s a more solid way to edit an fbx model and reimport it into Unity without messing everything else up, I just don’t know if this has anything to do with exporting the fbx from Unity (instead of just opening the .fbx file to a 3D application like 3DS Max), exporting from 3DS Max to .fbx or just tweaking any settings inside Unity.

Any hints I should know about?

Doesn’t anyone have any clue why this is happening?