Qt Mapping has issues when the vertical resolution is 1,536 or over (6 x 256, which is the size of each map tile). The problem manifests when the zoom level is between x.95 and x.20. That is, if the zoom level is between say 8.95 and 9.20 or 9.95 and 10.20, the maps are not rendered (the screen is left blank). When you zoom in or out of that range, the map is rendered correctly. If the vertical size is less than 1,536, everything works fine.

The issue is related to the number of tiles (in the Y direction only). If I set the tile size to 128x128 (in QGeoTiledMappingManagerEngine), the problem shows up with a smaller height (though around 900 pixels and not 768 as logic would dictate), and if I set it to 512x512 it doesn't show up at all (I can only go as high as 2,560 on my monitor).