I am not able to replicate the problem you're reporting. Make sure your CustomEntityProperty and CustomMetaDataProvider classes are properly configured.
I've attached a demo application as guidance for you, it's already configured to deploy to UWP (be sure to do a rebuild to restore NuGet packages).
If after reviewing the code and making necessary changes to your application doesn't fix the issue, please update the demo so that it replicates your problem and sent it back to us for further investigation.
Regards,
Lance | Tech Support Engineer, Sr.
Progress Telerik
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?
Explore the
Telerik Feedback Portal
and vote to affect the priority of the items