Even with very basic QML files, I am getting the following error on startup on the latest build of qtdeclarative

#0 QQmlDelayedError::removeError (this=0x2) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmljavascriptexpression_p.h:37
#1 QQmlComponentPrivate::complete (enginePriv=enginePriv@entry=0x5601809daf60, state=state@entry=0x560180bb4350) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlcomponent.cpp:1232
#2 0x00007f0a1e27d0af in QQmlComponentPrivate::completeDeferred (enginePriv=0x5601809daf60, deferredState=deferredState@entry=0x7ffce93af7d0) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlcomponent.cpp:1217
#3 0x00007f0a03c33dbe in QtQuickPrivate::completeDeferred (object=<optimized out>, property=..., delegate=0x5601809dccd8, engine=0x0) at /home/carl/kde6/src/qtdeclarative/src/quicktemplates/qquickdeferredexecute.cpp:166
#4 0x00007f0a03c27c32 in quickCompleteDeferred<QQuickItem> (object=<optimized out>, property=Python Exception <class 'gdb.error'>: Invalid reinterpret_cast
, delegate=...) at /home/carl/kde6/src/qtdeclarative/src/quicktemplates/qquickdeferredexecute_p_p.h:64
#5 QQuickControlPrivate::executeBackground (this=0x5601809dcae0, complete=true) at /home/carl/kde6/src/qtdeclarative/src/quicktemplates/qquickcontrol.cpp:765
#6 0x00007f0a03c32e10 in QQuickControl::componentComplete (this=0x7f09f40027c0) at /home/carl/kde6/src/qtdeclarative/src/quicktemplates/qquickcontrol.cpp:1997
#7 0x00007f0a1e3086ec in QQmlObjectCreator::finalize (this=0x560180c4e8f0, interrupt=...) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:1615
#8 0x00007f0a1e27cfea in QQmlComponentPrivate::complete (enginePriv=0x5601809daf60, state=state@entry=0x7f09f4003850) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/ftw/qbipointer_p.h:133
#9 0x00007f0a1e283679 in QQmlComponentPrivate::completeCreate (this=0x7f09f40037d0) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlcomponent.cpp:1342
#10 0x00007f0a1e284315 in QQmlComponent::completeCreate (this=0x560180c168a0) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlcomponent.cpp:1308
#11 QQmlComponentPrivate::createWithProperties (this=0x7f09f40037d0, parent=parent@entry=0x0, properties=Python Exception <class 'gdb.error'>: There is no member or method named size.
, context=<optimized out>, behavior=behavior@entry=QQmlComponentPrivate::CreateDefault, createFromQml=createFromQml@entry=false)
at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlcomponent.cpp:996
#12 0x00007f0a1e28463b in QQmlComponent::create (this=<optimized out>, context=<optimized out>) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlcomponent.cpp:936
#13 0x00007f0a1e25947b in QQmlApplicationEnginePrivate::finishLoad (this=0x5601809daf60, c=0x560180c168a0) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlapplicationengine.cpp:158
#14 0x00007f0a1e2596b3 in QQmlApplicationEnginePrivate::ensureLoadingFinishes (this=<optimized out>, c=<optimized out>) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlapplicationengine.cpp:185
#15 0x00007f0a1e259741 in QQmlApplicationEnginePrivate::startLoad (this=<optimized out>, url=..., data=..., dataFlag=<optimized out>) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlapplicationengine.cpp:112
#16 0x00007f0a1e259797 in QQmlApplicationEngine::load (this=this@entry=0x7ffce93aff80, url=Python Exception <class 'gdb.error'>: Invalid reinterpret_cast
) at /home/carl/kde6/src/qtdeclarative/src/qml/qml/qqmlapplicationengine.cpp:371
#17 0x000056015d208347 in main (argc=<optimized out>, argv=<optimized out>) at /home/carl/kde6/src/qtdeclarative/tools/qml/main.cpp:652