OK, so I feel like I am going around in circles here and nothing I have come across seems to replicate the same issues I am having - all slight variations.
So the back-story:
We have a number of labs to re-image at the start of each year. Due to software compatibility we tend to run one macOS behind the current one. This year we've been running 10.12.6 and are looking at moving to 10.13.6 for our 2019 academic year.
We have also had some new iMacs arrive that will be deployed to some of the labs - but not all! The new iMacs have Fusion Drives.
We are on JamfCloud running JSS v10.8
Now in the past when I have wanted to update our BaseOS, I usually install the current working one and do an in-place update, create a new DMG from the result using DiskUtility and booting from an external drive. Occasionally I have had to do a clean install of the OS we are wanting to move to - then configure it how we like, create the DMG from that. Regardless, I then take the new DMG and place it a deployment Configuration in JamfAdmin - do a complete NetBoot re-image on a machine and everything has worked out nicely.
However this time round, when the iMac has finished imaging and rebooted the machine would start to boot - Apple Symbol --> Progress bar and then when it is at about 75% I would get the 'no entry' circle with a line through it come up.
So I did some reading and thought, perhaps using DiskUtility to create the DMG is not the way to go with the new File System - maybe I need to use AutoDMG. So I tried that and it 'kind of' worked insofar as, I got a base OS installed, but instead of booting to it, the machine would then boot into RecoveryMode, and once I had selected the Startup disk, then it would boot to the very basic BaseOS (initially no admin account - added later via Jamf Imaging) Default Dock, System Prefs not set how we like etc.
However this was still not suitable for our environment.
I then did some more reading and thought that perhaps I needed to break the Fusion Drive, reformat the Macintosh HD to HFS+ and then create a BaseOS DMG.
Still no joy - getting 'no entry' circle again!
I tried erasing the destination disk using Disk Utility before running Jamf Imaging - and that took me to the Recovery Partition after reboot again. Then when I tried it a second time I got the 'no entry' circle again.
I'm really at my wits end as to what I 'should' be doing. APFS vs HFS+, Fusion vs Split Drive vs CoreStorage.
I need a workflow that is simple, reliable and consistent.
I know we will need to move to a 'DEP' based solution and we are in the process of doing so, however I do not have time to figure exactly how that all works at this stage.
So in summary:
JSS 10.8 via JAMFCloud
Netboot Imaging
A mix of Fusion Drives and non-Fusion drives
BaseOS of 10.13.6
Have tried both DiskUtility, AutoDMG & Composer to create BaseOS DMG.
Have tried both HFS+ and APFS DMGs
All either boot to 'no entry' circle or Recovery Mode
Oh and most of the discussions I have seen about similar issues are from earlier versions a few years ago.
All and any guidelines would be appreciated before I lose what little hair I have left.