I traced it back to two items
A. the USB kexts (used the ones from your EFI folder)
and
B. This patch for the caddy...
"Try adding this patch to Kernel patching, works for Catalina, not sure still for Big Sur
Identifier = com.apple.driver.AppleAHCIPort
Find = 40600200
Replace = 00000000
Comment = Patch Hotplug / Caddy"
Will upload the EFI that works shortly...