Hi Michale,
Thank you for contacting syncfusion Support.
We could not able to reproduce the issue "Binding is not working in SfNumericUpDown on Xamarin.Forms.UWP platform". We have prepared a sample based on your requirement, please download it from the link given below.
Sample link:
http://www.syncfusion.com/downloads/support/directtrac/general/ze/SfNumeric-287955112.zip If the issue persist at your end, please let us know with the sample change with the replication procedure for the issue occurs at your end.
Regards,
Selva Kumar V.