Mirroring not working with HIK-based rigs? (UE5's Manny/Quinn)

[LFA-GameplayMechanics]

Hi,
I cannot make the mirroring work with characters using the HIK rig, but I can mirror poses with free sample rigs, for instance, Endo V1 from anim_matt. I cannot figure out what causes this issue, I tried different settings, such as IK/FK switch, Mirror axis, pinning/unpinning controls transforms, rotation mode, etc. I also tried other HIK rigs without success (ActorCore, Metahuman Ctrl Rig).

To reproduce:

1. Open a scene with the rig (with or without referencing)
2. In Studio, create a folder for the rig, select all controls and create a Binding Pose, then create a Mirror Table from the binding pose
3. Create poses at frames 1, 15, and 31, then select all controls and save those poses in a new folder
4. Select all controls and try to apply mirrored poses for each pose at frames 8 and 19, and 25. I also repeated these steps selecting only the desired controls.

Results: Mirroring works with Endo, but Manny poses are getting undesired results. Sometimes, only feet are mirrored correctly. Sometimes feet transforms are swapped (see screenshot). Arms, when not ignored by the script, get unpredictable rotation values.

Comparing Endo and Manny rigs, both have Mirror orientation to Object, Y axis, posed with FK mode. Studio's settings is YZ plane. I tried with and without references, namespaces, and no avail.

I tested with Maya 2022 and 2023, Studio Library 2.9, 2.13 and 2.14.