Okay, after changing the section names from “Upscaler Settings | Nvidia” to “UpscalerSettingsNvidia” and the same for AMD, the issue appears to be gone!
Seems like maybe section names don’t support “|”, spaces, or maybe neither?
“FSRMode” is still saved as “FsrMode” for some reason…
I don’t foresee having time to work on this more until Monday, but I’ll report back here after I’ve had time to do some more testing…