Hi Renato,
Greetings from Syncfusion.
We are able to reproduce the reported issue with SfAutoComplete control in Xamarin UWP platform. We have considered this as a defect and logged a defect report. We will fix, and the fix will be included in our upcoming Volume 3 SP1 release which will be by the end of this month. [October 2018].
Regards,
Paul Anderson