Rig refuses to animate arms properly, rotates on wrong axis

I noticed during some testing that an R15 rig I created has somewhat stiff arms that rotate incorrectly

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This is how the rig was built. Building with the arms down to their sides did not change this issue.

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My avatar, for example, follows the default walk/run animation in the arms, whereas my rig doesn’t follow this animation at all. The arms will rotate around themselves only, not like my default avatar.

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Trying to fix the issue, I noticed the rotation was different between rigs, so after testing with my rig in a T-pose, I manually rotated the arms in my rig from to an A-pose. This did not solve the issue. The Motor6D joints’ Part0/Part1 follow the R15 Woman rig’s, so that’s also not the issue.

Is there something I’m doing wrong or is the plugin I’m using the issue? Something entirely different from my theories? Please let me know.

Have you tried this yet?