In the log snippet above, the iscsi disk is not set to auto mount, so it will have to be mounted manually. Not sure if that was intended.
Mounting of UD disks is done on the array started event - array disks are mounted. I believe this includes array, cache, and pool disks. The network might not be available at this time. As I understand the way this works, the iscsi device has to be mounted across the network before UD can mount it.
Remote mounts are delayed for up to 30 seconds before they are mounted and wait for the network to be ready. I'm reluctant to delay disk mounts until the network is ready because docker containers and VMs may need disk access before the network is available.
A little trick would be to enter this command in a User Script set to run at first array start:
sleep 2
/usr/local/sbin/rc.unassigned mount /dev/sdX or devX
Try to use devX and not sdX because sdX can change on a reboot. devX will always apply to the same device. Note: 'Dev 1' would be 'dev1', 'Dev 2' would be 'dev2', etc.
The sleep time might have to be adjusted depending on the server.