Greetings from Syncfusion,
We have analyzed your query. And we would like to inform you that when adding the ScrollView inside the TabItem content it will conflict with the Gesture recognizers between the swipe and scroll view. So, you can perform either Scrolling or Swiping at the time.
If you want to perform a Horizontal scrolling means, then you need to disable the Swiping between the views.
Muneesh Kumar G