I have the following callstack

              Qt5QuickRTILd.dll!QHash<QQuickPixmapKey,QQuickPixmapData * __ptr64>::remove(const QQuickPixmapKey & akey) Line 790   C+                Qt5QuickRTILd.dll!QQuickPixmapData::removeFromCache() Line 1164 C                Qt5QuickRTILd.dll!QQuickPixmapData::release() Line 1143         C                Qt5QuickRTILd.dll!QQuickPixmapStore::~QQuickPixmapStore() Line 949             C+ 

Code is: 

    // unreference all (leaked) pixmaps
    for (auto *pixmap : qAsConst(m_cache)) {
        int currRefCount = pixmap->refCount;
        if (currRefCount) {
#ifndef QT_NO_DEBUG
            leakedPixmaps++;
#endif
            while (currRefCount > 0) {
                pixmap->release();    // this is Qt5QuickRTILd.dll!QQuickPixmapStore::~QQuickPixmapStore() Line 949    C++
                currRefCount--;
            }
        }
    }

I think it is not allowed to remove the element of a QHash, where your iterator points to. This only happens if there is a  pixmapdata with pixmapStatus != QQuickPixmap::Ready.

In fact I get a crash afterwards.

Qt5CoreRTILd.dll!QHashData::nextNode(QHashData::Node * node) Line 614     C+                Qt5QuickRTILd.dll!QHash<QQuickPixmapKey,QQuickPixmapData * __ptr64>::const_iterator::operator() Line 394                C                Qt5QuickRTILd.dll!QQuickPixmapStore::~QQuickPixmapStore() Line 941             C+Exception thrown: read access violation.

d was 0xFFFFFFFFFFFFFFFF.

This happens in a unittest, where a async Quickimage is instantiated and shut down in a sequence.

IMHO this would fix the problem:

    // unreference all (leaked) pixmaps
    for (auto *pixmap : qAsConst(m_cache)) {
        int currRefCount = pixmap->refCount;
        if (currRefCount) {
#ifndef QT_NO_DEBUG
            leakedPixmaps++;
#endif
            pixmap->inCache = false;  // FIX                  
            while (currRefCount > 0) {
                pixmap->release();                                         
                currRefCount--;
            }
        }
    }