I am wondering if this can be reproduced. This first example Experience shows the dropdown working correctly. There is not an Action on the Map Widget to filter the data by map extent:
Then I copied the experience and set the Action to filter the data by map extent showing that the dropdown in the Filter Widget is empty:
See attached snapshots of widget settings.
Thanks for bringing it up and sharing the apps with us.
This issue is related to using Geometry and DistinctValues at the same time for REST services Query. We will follow up on it and see what we can do.