Hi Phu,
We have a similar issue regarding SelectedDate on iOS logged in our feedback portal, the reason behind is the same, although the scenario is a little bit different. You could follow the item below in order to get email notifications on status changes:
https://feedback.telerik.com/xamarin/1415568-selected-date-is-not-preserved-when-switching-viewmodes
I am sorry for any inconvenience caused.
Regards,
Yana
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