Could shoulders not being rotated for "up" correctly?

Having another go with VRoid Studio. Really hacky way I have layered a few files together, but got it to move a bit. I had to change forward/up for this character. But then all of the joints seem to be okay(ish), except the shoulders. It made me wonder if forward/up normalization was not happening for the shoulder joints.

Note: the same walk animation clip is being used on both characters. (It is the Start Preview button in the Animation Retargeting window).

I tried using Sequencer and dropping the timeline on there instead, but that was even more wonky. No arm joints worked, and character moved up/down rapidly face down.

I don’t know how much time this is worth investigating. I am hoping to clean up the hackery once the GLB root bone issue (previously reported with a copy of the character) is fixed. I am just trying to retarget that character. I merged together layers from different means of bringing the character in, so it is a bit weird the setup. But reporting just in case of interest.