Two OSX Installations, Two Boot Drives, only one working EFI?

Feb 14, 2020
Intel I7-4770k
GTX 1060
  1. MacBook
  2. Mac Pro
Mobile Phone
  1. Android
Hey all,

I've recently reinstalled my new Hack (the i7-10700k build). On my old system I had two physical boot drives (one main and one test bench), each with in individual OSX installation. Each drive had Clover, you could boot from either one an reach the Clover boot screen and boot either drive's OSX installation.

With OpenCore on my new build, I've got my two installations on separate drives. I can set my BIOS to boot from the Test Drive's EFI and it reaches the OpenCore menu fine and I can boot either drive. When I disconnect the test drive and set my BIOS to boot from the main drive, I just can't get OC to load or even be recognised. It just loops back to BIOS.

I've mounted the EFI partition of the main drive and exactly copied the EFI folder structure to it from the test drives EFI partition, i've even tried fresh installs. Nothing.

Any ideas why I'd only be able to boot from one of the drives EFI folders and not the other? Is it to do with the fact I installed the second instance of OSX (the main drive was second, the test drive was first) whilst the first was connected? The fact that my main drive shows up in BIOS implies that the EFI partition is being seen and the bootloader file recognised?