Without more information about your setup (SDK versions, dependency versions, etc), I'm unable to give you definitive answer. That being said, this looks similar to an issue that came up when you use Xamarin.Forms 4 with an unsupported version of Telerik UI for Xamarin.
You will want to update Telerik UI for Xamarin to 2019.2.708 to get the latest fixes for Xamarin.Forms 4.0 or 4.1. Alternatively, you can update Xamarin.Forms to v3.6 (the latest 3.6) to have full compatibility with UI for Xamarin.
If you still have trouble after updating, please open a Support ticket here
and share the project details so we can replicate. This will tell us if it's a new problem with XF 4 that needs to be addressed in an upcoming update.
Lance | Technical Support Engineer, Principal
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items