I was not able to replicate the issue, and the fact that one of your other apps is also working with the same code, indicates that this is a project-specific problem and not directly related to the DataForm. If you'd like us to help investigate your custom code, open a support ticket here
and attach the project. We will investigate further.
Update UI for Xamarin
We have a new release that contains fixes, update to 2018.2.620
and do a clean/rebuild cycle.
Common Xamarin Compilation and Deployment Issues
I would investigate typical Xamarin compilation and runtime solutions to see if it helps (e.g. delete bin/obj folders and rebuild, make sure the deployed project is a fresh build and not a cached assembly, close and re-open visual studio, etc).
Finally, I see that you've opened another forum post with a similar problem, where it works for one project, but not another, even though they have the same code. My feedback is the same int his case as well.
Lance | Tech Support Engineer, Sr.
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