After about a week, I finally have something that seems to work.
I copied the anims I wanted to retarget, and removed the tick for all three root options: EnableRootMotion; Force Root Lock; Use Normalized Root Motion Scale.
Then I change both source and target IK_Rig, where I added a pelvis chain since there isn’t one.
I kept the retarget root set to pelvis on both IK_Rigs.
In my IK_Retargeter, made sure the pelvis was set up Chain Mapping to point to pelvis.
Also in the IK_Retargeter, I clicked on Root and made sure it was set to Globally scaled, and Source Chain was set to root.
Then I retarget my anims.
I add Jog anim to my animation track and duplicate it so I have 2 one after the other.
In the jog animation I tick EnableRootMotion. I leave Force Root Lock unticked and tick Use Normalized Root Motion scale.
Root animation is moving character along in sequencer.
I then look at the last frame in the 1st jog animation, see which foot is touching the ground - it is the left foot, so in the next jog sequence I use Match with this bone in previous clip and match the left foot. Now my metahuman runs both cycles successfully.
If you match with pelvis, you will get snap back half way through the anim. Best to match the foot so the character continues.