QGIS » QGIS Application

QGIS 2.18 new install. One particular project crashes out instantly when trying to move the map canvas, or freezes. This is a fairly simple project with about 15 layers, only 5 of which are active.
One layer appears to be problematic - it is a polyline shapefile (saved out of QGIS from a DXF ASCII 2010 that I imported). This is styled by category (about 40 categories) of which maybe 2/3rds are active.

I created a fresh project & added the layers, testing the zoom as they were added and it was stable until I was just putting the finishing touches to the Composer when it started crashing out .

On advice from the OSGEO list, I removed all the plugins & these projects still crash.

GDB/bt report:
gdb -ex=r --args /usr/bin/qgis.bin
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
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Reading symbols from /usr/bin/qgis.bin...(no debugging symbols found)...done.
Starting program: /usr/bin/qgis.bin
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Warning: loading of qgis translation failed [/usr/share/qgis/i18n//qgis_en_GB]
Warning: loading of qt translation failed [/usr/share/qt4/translations/qt_en_GB]
[New Thread 0x7fffcd875700 (LWP 21610)]
[New Thread 0x7fffc7fff700 (LWP 21611)]
[New Thread 0x7fffc75cf700 (LWP 21612)]
[New Thread 0x7fffc6dce700 (LWP 21613)]
Warning: QCss::Parser - Failed to load file "/style.qss"
QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed: No such file or directory
[New Thread 0x7fffc65cd700 (LWP 21615)]
Warning: QFileSystemWatcher: failed to add paths: /home/jonathan/.qgis2//project_templates
[New Thread 0x7fffc5dcc700 (LWP 21616)]
[New Thread 0x7fffc55cb700 (LWP 21617)]
Warning: QLayout: Attempting to add QLayout "" to QgsPanelWidgetStack "mWidgetStack", which already has a layout
[New Thread 0x7fff5e7bc700 (LWP 21636)]
[New Thread 0x7fff5df6d700 (LWP 21642)]
[New Thread 0x7fff5d76c700 (LWP 21643)]
[New Thread 0x7fff5cf6b700 (LWP 21644)]
Warning: QPainter::begin: A paint device can only be painted by one painter at a time.
Warning: QPainter::setRenderHint: Painter must be active to set rendering hints
Warning: QPainter::setBrush: Painter not active
Warning: QPainter::setPen: Painter not active

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fff5df6d700 (LWP 21642)]
0x000001c500000231 in ?? ()
(gdb) bt
#0 0x000001c500000231 in ?? ()
#1 0x00007ffff5086d21 in QPainter::end() ()
from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#2 0x00007ffff610ddd0 in QgsSimpleMarkerSymbolLayerV2::prepareCache(QgsSymbolV2RenderContext&) () from /usr/lib/libqgis_core.so.2.18.4
#3 0x00007ffff610e34b in QgsSimpleMarkerSymbolLayerV2::startRender(QgsSymbolV2RenderContext&) () from /usr/lib/libqgis_core.so.2.18.4
#4 0x00007ffff6165573 in QgsSymbolV2::startRender(QgsRenderContext&, QgsFields const*) () from /usr/lib/libqgis_core.so.2.18.4
#5 0x00007ffff609bb2c in QgsCategorizedSymbolRendererV2::startRender(QgsRenderContext&, QgsFields const&) () from /usr/lib/libqgis_core.so.2.18.4
#6 0x00007ffff6450e2a in ?? () from /usr/lib/libqgis_core.so.2.18.4
#7 0x00007ffff631a4f7 in QgsMapRendererParallelJob::renderLayerStatic(LayerRenderJob&) () from /usr/lib/libqgis_core.so.2.18.4
#8 0x00007ffff631b7e0 in ?? () from /usr/lib/libqgis_core.so.2.18.4
#9 0x00007ffff631b837 in ?? () from /usr/lib/libqgis_core.so.2.18.4
#10 0x00007ffff631bc1d in ?? () from /usr/lib/libqgis_core.so.2.18.4
#11 0x00007ffff5a93005 in QtConcurrent::ThreadEngineBase::run() ()
from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#12 0x00007ffff5a94fee in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#13 0x00007ffff5aa132f in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#14 0x00007fffee1e8184 in start_thread (arg=0x7fff5df6d700)
at pthread_create.c:312
---Type <return> to continue, or q <return> to quit---
#15 0x00007ffff458e37d in clone ()
at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
(gdb)