Hi Morgon,
Thanks for contacting Syncfusion Support.
We have analyzed the reported problem based on the provided information and suspect that this is due to improper recognize of visual designer.
We suggest you try to clean and rebuild the project application or close(remove bin & obj file) and reopen the sample, it may be a chance to resolve this problem.
If you are still facing the same problem then please download the sample from below link which we have used to test this scenario and let us know if anything need to be modified in this sample.
Regards,
Durgadevi S