My custom application settings page does not load, wait indicator does not terminate

Question

I followed this guide to implement a page with settings for my ArcGIS Pro AddIn (for 2.9.x):

https://github.com/esri/arcgis-pro-sdk/wiki/ProGuide-Custom-settings#custom-application-settings

When I open the Options dialog, it works on my machine.

When I install the Add In on the customers machine, and I open the Options dialog, there is a wait indicator which does not stop. My page is never shown. What can be wrong here?

The version of Pro is exactly the same on both machines:

Stefan_Offermann · Accepted Answer

The problem was a Setting of type Date, which had no default value:

After setting a reasonable value, the Options page loaded:

This line of code failed in the InitializeAsync() method:

StartDate = _startDateOrig = Settings.Default.StartDate;