I have the same issue on SteamVR. My current working hypothesis for the root cause is that both SteamVR and Oculus software are trying to correct twice the “inherit to VR lenses” lens distortion. If that’s the case then we can’t do a thing as SteamVR should pass the image unaltered to Oculus software and currently it seems not to be doing that.
Workaround: Use Oculus runtime.