Comment 1 for bug 1758282

This seems to me to be an upstream bug. The grow command starts the systemd unit, but doesn't enable it to be persistent. The md device names can change after reboot (if an additional array is connected whilst the system is off), therefore I think upstream udev rules should be improved to detect arrays that need mdadm-grow-continue@.service, and trigger that unit via SYSTEMD_WANTS stanza in the udev rules.

Could you provide a dump of /sys/devices/virtual/block/md126/md after reboot, when you expect the mdadm-grow-continue to resume? (assuming md126 is the one undergoing reshaping)

I hope that, e.g. /sys/devices/virtual/block/md126/md/sync_action is "reshape" and /sys/devices/virtual/block/md126/md/reshape_position is not "none".

Then it should be trivial to adjust the udev rules, to kick off mdadm-grow-continue@.service, based on those sysfs attributes on boot.