Please clarify the last set of instructions according to my bolded responsemy guess is that's a leftover from a previous boot (the subvol-dirs got created - thus the subvols cannot be mounted)
after reboot (without any containers starting):
* check whether the pool SSD is imported (does it show up in the `zpool status` yes
* if yes - is /SSD mounted (`zfs get all SSD |grep mount`) yes
** if yes - are any of the subvols mounted (`zfs get all SSD/subvol-102-disk-1 |grep mount`) yes
** if yes - is there any content inside? no
* if no - are there any (empty) directories in /SSD? all the subvols are empty directories
** if yes - `rmdir` them and reboot do you mean reboot in this "failed" state without mounting the subvols first?
I hope this helps!