I think this may be a bug so I wanted to let you know about this.
I was trying to set up the SFListView with a Horizontal orientation and then set the span count within the Grid layout and was only getting a single row. I couldn't figure out what was happening until I did some testing. It looks like by setting both, the orientation is transposing how the layout is handled as it appears that setting GridLayout.SpanCount also sets the orientation to horizontal (IE they cancel each other out somehow)
To Replication this, get an item source of a few items and then use:
<sflistview:SfListView ItemsSource="{Binding YourSource, Mode=TwoWay}" Orientation="Horizontal">
<sflistview:SfListView.LayoutManager>
<sflistview:GridLayout SpanCount="4" />
</sflistview:SfListView.LayoutManager>
</sflistview:SfListView>