Using the UEFN workflow where you have an animation and you use the internal tool to retarget and export its retargeting, everything works correctly (animations retarget correctly) however the hand IK goals have an offset that causes the custom guards to not hold the weapons correctly, as shown below.
I have attached the tutorial I followed for the repro, with the extra steps of setting up an NPC guard and setting that skin as one.
Bring Mixamo Animations into UEFN | Epic Developer Community