CharacterMesh has to have 'Simulate Physics' enabled if you'd like to AddImpulseAtLocation

Apologies for the necro posting, but just in case someone else comes across this problem:

If you’d like to keep EnablePhysicsInteraction true on your Character Movement Component, and have physical animation, then on BeginPlay you need to tell the character mesh to ignore the capsule when moving.

ignore-when-moving

Very irritating thing to track down.