Hi,
In the latest 2019.3.917 release there is a scripting error if setting animation duration to zero. It happens on open. This error is also in your demo (if setting duration to 0):
https://demos.telerik.com/aspnet-ajax/datepicker/overview/defaultcs.aspx
This scripting error was not present in earlier versions.
The effect of this error is that the opened event isn't raised!
Regards
Andreas