Comment 11 for bug 1850130

I think there are multiple issues here. If it's just multipath, that issue should be resolved by adding After=multipathd.service to zfs-import-{cache,scan}.service.

For other issues, I wonder if this is cache file related. I'd suggest checking that the cache file exists (I expect it would), and then looking at the cache file (e.g. strings /etc/zfs/zpool.cache | less). I suspect the issue is that the cache file has only the rpool. I'm not entirely sure why that is happening.