Greetings from Syncfusion.
By default, the focus is always set to the first element in UWP platform. You can observe the same behaviour with Entry instead of the SfTextInputLayout.
Please refer the reference link to avoid this issue - https://stackoverflow.com/questions/42231163/is-it-possible-to-stop-the-first-entry-getting-focus-in-a-scrollview-in-xamarin/42245601
Please check this and let us know if you need further clarification on this.