I tested this bug in your sample project for Xamarin.Forms 'SfMaskedEdit'.
When I type in a value in one of the MaskedEdit controls, this value appears two times. (See the attached screenshot).
All the following keybord inputs seem to be ok and appear only one time as expected.
As you can see in the 'Amount' field of the example view, this is the output when i constantly press '1'. Looks strange as well.
Like that, I'm not able to type in a single char.
Btw, my keyboard works fine, tested it in different editors. This problem only appears when I type in the MaskedEdit control.