When I use my Fireface 400 with Windows 10 the Software Playback channels route as a mono signal (left/right summed) to every single right hand output.

This does not happen when I use it with my 2011 Macbook Pro running Sierra. So I'm pretty certain it's not a hardware issue.

The other bizarre detail is that upon first booting up, the main output also just gets a mono sum to the right channel *but* this goes away if you adjust the stereo width parameter at all. I've tried a reset mix->total reset but that does nothing for the issue.

Here's a gif screencapture of it happening. https://imgur.com/a/KMb3rxH

My windows machine gets firewire from a PCI card. I've tried both the firewire 800 outputs on it (obviously a convert to 400 type cable) with the same results.

I should note that I have used this PC with this interface successfully years ago. It started happening at some point but I wasn't using the other outputs at the time so I just turned the level down and forgot about it and figured maybe it was a bad software version that would end up fixed at some point. The hard drive died eventually and now I'm resetting it up with the intention of using multiple outputs and the issue is persisting even through a fresh Windows installation.

Any help is greatly appreciated, I'm quite baffled.