Thanks both for your replies. Here are a couple of screenshots :
This is from one of the 12 ipads I added recently, note they say they are not Supervised. All other 77 devices show as supervised, but also show the MDM is non compliant as above.
Since I last posted, I have generated a new MDM Push certificate and uploaded etc in the knowledge that I will need to un-enroll and re-enroll all the devices with a reset (I think?!)
My gut feeling is that the 12 ones that flagged up the problem originally were added through Apple Configurator have a setting error ( perhaps I set them up using server info in AC2.5 with the wrong Meraki certificate too if it was out of compliance)
I am ready to collect all the devices in and do the reset if that's my best bet, but having tried resetting one of the new ones, it still shows up as a temporary MDM push certificate. I don't understand!