QGIS » QGIS Application

In my QGIS opentopo project file (see www.opentopo.nl for rastered results) I use two label-layers for OSM (in PostGIS) road labeling: one for the major roads and one for the minor roads. These layers have two mutually exclusive filters on the OSM data set.
I use an invisible index shapefile to generate an atlas of TIF raster images. The shapefile contains square polygons denoting the extents per page. I've checked that the geometries are valid.
Until QGIS 2.10, the Atlas print composer generated all TIF raster images without any problems.
In QGIS 2.12, the Atlas print composer hangs at a particular atlas page (always the same one). It doesn't crash but seems to come into a deadlock; after 24 hours still no result. By eliminating map layers one-by-one I've identified the two OSM labeling layers to be the issue. The atlas composer works fine with none or one of these layers activated, but hangs when both OSM road labeling layers are activated. This wasn't the case in previous versions.
I've tried changing all kinds of labels parameters (placement; priority; repeating labels, etc.) but no improvement.
I've tried to vacuum and reindex the OSM PostGIS database, but no improvement.