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My set-up is Linux Mint 17.1, 32- bit system, QGIS 2.8.1-Wien.
I have a map with few layers including OpenCycleMap as a basemap. In Print Composer the extent of the map is 32.5km x 22km square and the print page size is A1.
I am exporting from Print Composer to a large PNG image file of about 220Mb (container size) at a resolution of 200 DPI.
Everything exports to the image file fine, except OpenCycleMap. It does not appear to have enough time to download from the server. There are therefore many missing background map tiles.