Apple's Profile Manager (MDM) is suddenly unable to updates settings on enrolled iPads
So I managed to fix this here, but the reason it's failing is really strange.

I removed the Security &amp; Privacy payload from the settings, which mostly consists of OS X settings, but also has "Allow sending diagnostics and usage data to Apple" setting for both OSX and iOS. I had a sneaking suspicion that this was somehow messing up since it mostly consisted of OS X settings, and turns out I was right.

Now WHY this would mess it up is baffling to me, I'll file a radar with Apple here as it's clearly not intended to fail as this payload belong to the OS X &amp; iOS section. (And either way you can have both iOS devices and Macs in the same group, so OS X specific settings shouldn't cause problems for the iOS devices).