Try to set up a “Blend Space” with different mixamo animation. This will smooth up your charaters movement.
I think you speeded up the animation in Maxamo aswell. Just speed it up with Unreal or the Blend Space itself to make sure the speed is realative to the animation.
If you have height problems, look for “Translation Retargeting” or just put the Charater down to the floor by moving his whole mesh a bit down.