Azure Mobile Center: build issue for iOS on Xamarin.Forms project

Question

I've started to develop a Xamarin.Forms app 2 months ago.

For this, I've chosen to use GrialKit for the UI, and Visual Studio Mobile Center for CI. During the first weeks all worked fine: I could distribute my test versions thanks Mobile Center.

But I had to install the 2.4.0.269-pre2 package version of Xamarin.Forms to integrate Iconize to my app. Since this, I'm no longer able to build iOS releases on Mobile Center. I got errors like:

"/Users/ci/agent/vstsagent/_work/1/s/Xxx/Xxx.iOS/Xxx.iOS.csproj" (Rebuild target) (1) -> (_CompileToNative target) -> MTOUCH : error MT4109: Failed to compile the generated registrar code. Please file a bug report at http://bugzilla.xamarin.com [/Users/ci/agent/vstsagent/_work/1/s/Xxx/Xxx.iOS/Xxx.iOS.csproj]

11 Warning(s)
1 Error(s)

Time Elapsed 00:03:25.71

##[error]Xamarin.iOS task failed with error Error: /Library/Frameworks/Mono.framework/Versions/Legacy_5_0_1/bin/msbuild failed with return code: 1. For guidance on setting up the build definition, see https://go.microsoft.com/fwlink/?LinkId=760847.

I can build the app on my own iPhone from Visual Studio (Windows) or Visual Studio for Mac without any problem: so the problem comes probably from Azure Mobile Center.

I also tried to update the package to the latest version (2.4.0.282) but this didn't change anything...

Would you have any suggestion or explanation?