This is a bug when using MaskedEdit in UWP.
(1) Enter the maximum number of characters in SfMaskEdit in which the Mask property is set.
(2) In the state of (1), put the focus on the end and right-click → "Paste" to paste the character.
(3) With the pasted state of (2), select all the character strings in the SfMaskedEdit and press the Delete key.
↑The app freezes after the operation in (3).
paste by Ctrl + V is disabled, and I can paste only from the right-click menu.
So I think it's a bug that we can paste from right click.
This bug also occurs in Syncfusion Essential Studio for Xamarin.