As I recall, Gigabyte MoBos expect the boot drive to be at 0.
The manual doesn’t say as much, but that’s what I assume too, whether single ssd/hdd or multiple. The question is what’s different about port 0. While I was traveling in September, a final version came out for the beta BIOS I’ve been running. I’ll check that, but unlikely it’s related. Everything else is up to date.