Have resolved this by a little 'trial and error'
I removed the agent requirement from the 'all' OS group.
I trashed the user pages I had created and set them up again for MAC_ALL and All.
Added the agent requirement back in for ALL and exempted MAC_ALL from this requirement.
Seems to work ok, only odd glitch is MACOSX devices are being served the MAC_ALL user page even though they should not be.
The agent requirement for MACOSX is still enforced though.
Looks like this new upgrade is a little flakey