Animation Issue

Hi,

I'm currently working on a game with Unity. We are a team of 4 students and this is our first experience with this kind of work. We're having an issue with the animation of one our avatar. We have made an animation with Blender. When running on Blender, the animation doesn't appear to have any defects. When imported into Unity, if the avatar is in "Legacy mode", still no issues but when we switch to "Humanoid Mode", the avatar starts having some problems. The feet are "floating" above the ground and when the legs have to flex, the feet are coming up instead of the pelvis coming down.

Does anyone have any thought on this ? We're running out of ideas.

Thanks for reading me, Best wishes.

Ps : The four of us are developer, we don't have any designer or 3D specialist on the team. Ps2 : Apologies for my English, I'm from Belgium.