I created an app from data in a custom SP list with several People columns.
In the app, the people picker worked for some of them but not for others.
All their properties (in the app) were the same.
Then I figured out that it only works if the property of the Person/Group column in SP is set to "People and Groups".
If "People Only" is selected, an Edit Lookup control will still work, but not an Edit Selection control.
Is this a bug or by design?