Although this question is a bit old, some might still find my answer useful.
I have found the following the hard way implementing it myself
The problem occurs with animations that are not animating the IK bones (like the default UE animations).
You’ll either have to change/update your animations to use the IK bones or ‘hack’ the following:
- Perform a velocity check in the IK BP where you only apply Ik when velocity is 0.
- Enable/disable IK using animation notifies.
Hope it helps.