This is the stack trace:

2 qt_message_fatal qlogging.cpp 1364 0x7fffedd28b68
3 QMessageLogger::fatal qlogging.cpp 669 0x7fffedd2a4d8
4 qt_pixmap_thread_test qpixmap.cpp 76 0x7fffee7535b7
5 QPixmap::QPixmap qpixmap.cpp 111 0x7fffee753554
6 QPixmapIconEngine::pixmap qicon.cpp 282 0x7fffee7658c2
7 QIcon::pixmap qicon.cpp 791 0x7fffee7677c7
8 QIcon::pixmap qicon.cpp 727 0x7fffee7676e8
9 QXcbWindow::setWindowIcon qxcbwindow.cpp 1362 0x7fffe60cc68a
10 QXcbWindow::create qxcbwindow.cpp 508 0x7fffe60c89f1
11 QXcbWindow::QXcbWindow qxcbwindow.cpp 210 0x7fffe60c7249
12 QXcbIntegration::createPlatformWindow qxcbintegration.cpp 182 0x7fffe60b4142
13 QWindow::create qwindow.cpp 494 0x7fffee6d8124
14 QWindowPrivate::setScreen qwindow.cpp 370 0x7fffee6d80c4
15 QWindow::setScreen qwindow.cpp 1629 0x7fffee6dad76
16 QWindow::screenDestroyed qwindow.cpp 1637 0x7fffee6daddd
17 QWindow::qt_static_metacall moc_qwindow.cpp 403 0x7fffee6dc44b
18 QMetaObject::activate qobject.cpp 3680 0x7fffee0dcc43
19 QMetaObject::activate qobject.cpp 3546 0x7fffee0dc0ed
20 QObject::destroyed moc_qobject.cpp 205 0x7fffee0d3f0c
21 QObject::~QObject qobject.cpp 901 0x7fffee0d36bc
22 QScreen::~QScreen qscreen.h 64 0x7fffeeb19285
23 QScreen::~QScreen qscreen.h 64 0x7fffeeb19235
24 QScreen::~QScreen qscreen.h 64 0x7fffeeb19259
25 QPlatformScreen::~QPlatformScreen qplatformscreen.cpp 65 0x7fffee6b73f5
26 QXcbScreen::~QXcbScreen qxcbscreen.cpp 209 0x7fffe60c4f6c
27 QXcbScreen::~QXcbScreen qxcbscreen.cpp 207 0x7fffe60c4eb9
28 QXcbConnection::~QXcbConnection qxcbconnection.cpp 413 0x7fffe60aa00b
29 QXcbConnection::~QXcbConnection qxcbconnection.cpp 390 0x7fffe60a9ea9
30 qDeleteAll<QList<QXcbConnection*>::const_iterator> qalgorithms.h 323 0x7fffe60b5c23
31 qDeleteAll<QList<QXcbConnection*> > qalgorithms.h 331 0x7fffe60b53a6
32 QXcbIntegration::~QXcbIntegration qxcbintegration.cpp 177 0x7fffe60b4075
33 QXcbIntegration::~QXcbIntegration qxcbintegration.cpp 176 0x7fffe60b4029
34 QGuiApplicationPrivate::~QGuiApplicationPrivate qguiapplication.cpp 1328 0x7fffee6c7d26
35 QApplicationPrivate::~QApplicationPrivate qapplication.cpp 188 0x7ffff00c9f17
36 QApplicationPrivate::~QApplicationPrivate qapplication.cpp 185 0x7ffff00c9e69
37 QScopedPointerDeleter<QObjectData>::cleanup qscopedpointer.h 62 0x7fffee0e480e
38 QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::~QScopedPointer qscopedpointer.h 109 0x7fffee0e47c8
39 QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> >::~QScopedPointer qscopedpointer.h 107 0x7fffee0e0ce5
40 QObject::~QObject qobject.cpp 1034 0x7fffee0d3e96
41 QCoreApplication::~QCoreApplication qcoreapplication.cpp 810 0x7fffee087153
42 QGuiApplication::~QGuiApplication qguiapplication.cpp 590 0x7fffee6c55b8
43 QApplication::~QApplication qapplication.cpp 781 0x7ffff00cb270
44 QtSingleApplication::~QtSingleApplication qtsingleapplication.h 69 0x5c4b55
45 QtSingleApplication::~QtSingleApplication qtsingleapplication.h 69 0x5c4b05
46 QtSingleApplication::~QtSingleApplication qtsingleapplication.h 69 0x5c4b29

It looks like somehow the destructor wants to create a new platform window which failes. The fatal message is:

QPixmap: Must construct a QGuiApplication before a QPixmap