I did update the zfs cache-file as you instructed on all my pools and that fixed it - ssd2 now got mounted during boot and containers would automatically start again.
Thanks for your support, much appreciated!
I think I found the problem. The containers where using a ZFS dataset which was not mounted. When I manually mounted them - my containers started as normal.
However, why my ZFS dataset is not automatically mounted is unknown to me. But that is something for another topic :)
I'm having the exact same problem and indeed it says:
Script exec /usr/share/lxc/hooks/lxc-pve-prestart-hook 104 lxc pre-start produced output: unable to detect OS distribution
I did a restore of a backup I had of the container and it started. Unfortunately, after a reboot of the proxmox-host...