Hmm, I have to say it looks to me like some kind of bug in WMR. You know I don't run away from bugs but this is different. Specially as Microsoft is involved, it seems likely to have bugs. Though of course is could be in the HP software too.
LFS goes though OpenVR and has been working correctly for a long time. Now a new headset comes out and Microsoft has something to do with the interface, if I understand correctly, and now it doesn't work in one particular headset.
From your screenshot, you already show that LFS is generating the correct image. But some part of the interface or driver software is not projecting that correctly onto the final screen.
I think the best thing would be to ask HP or Microsoft if they can recognise the problem. Maybe their software makes certain assumptions. For example do they assume each eye's view is rendered onto a different texture? Some programs do that, but LFS renders both eyes onto a single texture (left and right side) which is allowed by the specification.
I'm not saying that's the problem, I'm just making the point that some programs may do things in a slightly different way and maybe their software assumes one way.
One more thing we could do, if you would post the OpenVR.log here I could have a quick look in there and see if anything looks strange.