I realize this is an old thread, but I had a similar problem, and here’s another case that might help someone:
The short answer is: check the height of the skeletal mesh in your BP, relative to the bottom of the capsule.
Montages for certain animations worked 100% on my player, but my npc was floating off the ground. Turns out, I was stupid and in my npc character BP the skeletal mesh was +10 higher on the Z.
However, it doesn’t answer how to properly fix the specific animations in question. Possibly due to IK (or retarget?), since the ones in question were mixamo conversions, and ones from epic didnt have that problem.