Same thing happened to me. The problem turned out to be that I had the boot9strap folder in the wrong place. If it's not in the root folder for your SD card, make sure you put it there. If that doesn't fix it, maybe someone else has an idea.
I finally modeled and 3d printed the new HDD cages I need in order to build my 2nd NAS. Original ones don't fit the mounting holes on the hdds I'm using. Been sitting on this project for over 2 years smfh
Also another 70TB going in the front mount drive bays of this server. 182tb raw, going to probably use a zfs RAID-Z3 for 3 parity disks, so 140TB usable
I could claw back 14tb by only doing 2 parity disks but I feel like with 13 disks in the RAID I'd be kind of pushing my luck on rebuild time if I encounter a disk failure