I don't know if it has something to do with the San / Disk Policy but it sure looks like it.
Normal operation is 0,
boot your PE open a CMD box and type
Diskpart <enter>
automount <enter>
You will get the current status... You will probably get that it is enabled...
You can force Mountmgr to mount disks with the registry.
Use the addition plugin
RegWrite,HKLM,0x4,tmp_System\ControlSet001\Services\MountMgr,NoAutoMount,0
But... Your issue can be Driver related because Windows default is to load all new disks.
Can you try it on another computer to confirm that the current build you have behaves correctly.
Try unplugging the SSD and do a test boot see if the others are mounting properly,
Make sure that the exported Drivers Matches your build. Try a build without integrated drivers.
If it works, Unplug all other disks and troubleshoot the SSD alone.