I'm not sure if there is a fix for this, or if I am encountering a bug. I have 2 layers. The base layer is the XYZ Tile for OpenStreetMap and the top layer is a 1-channel raster, set to 50% transparency.
The problem is that when I zoom in too much or export it to an image using the Print Composer, it drops sections of the OSM tile. Zoomed out, looks ok:
When I export to image or pdf, it always renders it with the missing tile sections. I also see this problem with the zooming when I am in the main QGIS window.
Possibly related to this post?