USB Clover won't boot with one of my HD attached

[Nodarkthings]

The title says it all: I have to detach my most recent HD for Clover to launch from USB key, otherwise it doesn't even arrive at Clover's GUI.
No issue when my SSD or two older HDs are connected!
The only thing I can think of is that the HD has a few ZFS pools/partitions on it, but it doesn't seem to have anything bad — I boot from any MacOS partition on it, I've repaired any possible problem with Disk Utility, TechTool or DiskWarrior... no problem. No SMART errors neither.
Any idea? Could it be due to the sole presence of ZFS even if the first partitions are HFS+? What can I check?

EDIT: Now that I think about it, I also have a ZFS pool on my SSD and the Clover USB key boots with it attached, so ZFS has nothing to do with it... I guess I should reformat that HD and see what happens, but what a bummer, with all my carefully crafted partitions...

 

[Adrian B]

Apple is getting very touchy about other operating systems, folk been having issues with grub of late when dual booting. I don't know if this is Apple 'improving security' or what is going on.

If you are trying to install on this disk, then you may not be able to. If you wish to install on another disk, then remove ALL other drives while you install macOS.

 

[Nodarkthings]

Thanks but I've been using OpenZFS on Mavericks for years with no issue, and this is much probably a Clover (or hardware) issue as the USB key contains only Clover and no installer.
I'm booting with no issue on the OSes on that HD using Chimera and others on the other HDs using Clover (10.9 and 10.11) or Chimera (SSD 10.9).

P.S.: I already succeeded in installing 10.11 and 10.13 on other HDs. I'm just trying to make a SOS USB key.
But the issue is present also with the Unibeast key I've created for Hi Sierra...

Edit: I've activated the Debug option in Clover but it hasn't been written... I bet the reboot happens even before Clover has time to log anything.