Ah HECK. I've been aware of this issue for a while to be quite honest, but I literally do not know how to fix it. In Blender the rigging appears like it does on the left, but when exported appears like the busted version on the right.

@User You can if you wish. I already linked them on the discussion page I made, though I don't even know if he's seen the discussion page at all.

Would you like me to link the screenshots?

@User, I have made a discussion page on the addon page, but he hasn't said anything yet. I made these to show him the issue on said page. Is there a better way to get into contact with him?

have you reported this issue with Fission?

The knee and elbow bones don't properly rotate from what I can tell.

I don't know why the Octoling models do this. Mine has always done this kind of stuff.