Can you please upgrade to the previously mentioned version: 2.3.4.247 ?
The thing is, we don’t customize anything. Xamarin Studio is installed on the VMs using the official installer, and updated every week with the Xamarin Studio built in updater. If there’s anything we can do/fix please let us know!
One more note: the Xamarin Archive step now has support for specifying the build tool; if you use msbuild locally on your Mac instead of xbuild you can now set that on the Step (Xamarin Archive v1.4.1). I think this definitely worth a try.