WeekDay not working in CMS 11.3.2

Description

Steps to reproduce

1. Create a PageType with the Core property WeekDay like below:

   public virtual Weekday ValidDays { get; set; }

Actual: When going to all properties mode in the edit mode, the following property is not being rendered properly.

Expected: The property should render with a button that allows the editor to choose which days to specify.
This seemed to be working in CMS 10.x.x but stopped working in CMS 11.x.x.