I had the same problem when trying to import Anima Project to UE 4.27.
In Anima, when I added a " Talking group | 4 people" to the anima scene, there’s this one green shirted guy by default ( cman0204m4 ). Which has an invalid walking animation applied on (although it’s Idling in the group).
I ungrouped the 4 people with right click, selected the green shirted guy and changed his ‘Locomotion Walk Clip’ to something else.
I noticed that some of the other characters has invalid animations in some groups aswell. Just ungroup and change the animations.
Hope this helps.