maybe a misunderstanding - the issue is that, seemingly at random, there is no sign of the disks in `diskutil list` and then a few reboots later, there is. this is a low-level MacOS issue...
on a clean Mojave install, before the zfs kext is installed, MacOS offers me to `initialize` the disks if they are recognised by MacOS. on this basis I do not think zfs is the issue, which, FWIW, was updated for Mojave long ago and is has been stable for me on my other system.
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I have now been able to test, with the NVMe drive removed and only a SATA boot drive and 1 8TB SATA disk - the same issue persists. The boot drive is recognised and boots, attached to "Generic AHCI Controller" without AHCI kexts and "Intel 20 Series Chipset" with AHCI kexts. The 8TB SATA disk does not show up after many reboots...
To be clear, the SATA 8TB disk does not appear in `diskutil list` most of the time - and it seems that when booting from a SATA drive on the motherboard, not at all. I don't know what to make of that.
this would appear to also rule out NVMe is being the issue.