It happened on version 2.6 and I was told it was my version that was the trouble, so I reverted to 2.2. The odd thing is, that it will usually work fine the first time I open the map, but it seems like with each additional use more white squares pop up. This is happening with the OpenStreet and OCM layers. It does not seem to happen with other layers.
Any thoughts?
The reason for the missing tiles is that the tile server is responding too slow if it suffers heavy load from other users. Unfortunately, there is no option in the plugin to extend the timeout.
You can try increasing the values under Settings -> Options -> Network tab; or simply move around the whole canvas to activate a reload of the tiles.
Or use another tile server, like Mapquest. But they might not have the OpencycleMap designed tiles.
Apart from that, I suggest to set the project CRS to the native projection of the tiles, that is EPSG:3857.
