R Class issue - unable to locate management server

 R Class issue - unable to locate management server

All, have a really strange issue, been going on now with wyse support for almost 2 years

We have wdm 4.9.1 and four types of thin client devices, C,R,X and Z classes.

All classes work perfectly with WDM except the R classes (R90LE7)

I am trying to do a Get Image task. The R classes check into WDM fine and I am able to tell it to get image. It successfully prompts to update now or 5 minute delay. Issues start when it boots back up... it can't find the management server. It tries local registry search, DHCP and DNS-SRV but eventually times out. Sometimes it prompts for me to manually enter client ip information, wdm server address, protocols etc but still goes no further. Either way, it never works.
We have the correct dhcp tags setup, DNS records and also all discovery options selected in WDM. The client has all the latest boot, HAgents and image builds, although have tried many combinations of these.
REMEMBER, all other class devices work fine and start pulling or pushing images near immediately!

Even stranger, we built a replica of our environment for testing, consisting if:
Restore of our live domain controller with its DNS and dchp roles
Built a virtual environment and restored our live WDM server virtual machine
Restored our live secondary virtual DC which has dhcp and DNS too. (Had to remove it as a DC though due to replication errors, but still functioning as DNS and dhcp)
Connected together via an extreme networks switch (same brand as live network) and configured vlan ports as close as we could to live.

R CLASS WORKS ON TEST NETWORK! :-S
Only differences are virtual environment is on a hyper v 2012 host using SMB 3.0 storage to access the vhd's (whereas live is 2008 R2 using iscsi SAN)
Secondary DC is no longer a DC but still DNS and DHCP.

Bit lost now where to go with this. Has anyone else experienced this or have suggestions where else I could check?