zfs zvols not showing up in /dev/zvol after reboot

[aktivb]

I have 2 zfs zpools, after rebooting the zvols/block devices of one of them does not show up in /dev/zvol.
They exist in /sys/block. zd0 through 48 does not get links in /dev/zvol, zd64 through 128 does.
udevadm trigger/settle manually will create the links.

dmesg gives me two 'systemd-udevd used greatest stack depth' and one 'zpool used greatest stack depth' lines.
I have udev-212-r1. I had the same issue with udev-208.

How can I debug/fix this?
What is it that udev does during boot that's different from my manual trigger/settle?