I solved a long annoying boot-problem happened in the systemd-async-boot-process.
Adding a sleeptime in
/lib/systemd/system/systemd-udev-settle.service by adding
ExecStartPre=/usr/bin/sleep 5 to the
[Service]-Section, gives the system 5 sec. more time to load the zfs-module and import the pool before it tries to remount root to the real directory on disk.