@David: is this related to one of the recent changes regarding support for Qt 5.9?

*** Bug 380006 has been marked as a duplicate of this bug. ***

*** Bug 381331 has been marked as a duplicate of this bug. ***

Plasma 5.10.1, kde libraries 5.35.0, fedora 26 beta:

(gdb) bt full
#0  0x00007ffff771d9ae in org_kde_plasma_surface_set_position (y=<optimized out>, x=<optimized out>, org_kde_plasma_surface=<optimized out>)
    at /usr/src/debug/kwayland-5.35.0/x86_64-redhat-linux-gnu/src/client/wayland-plasma-shell-client-protocol.h:351
No locals.
#1  KWayland::Client::PlasmaShellSurface::setPosition (this=0x5555559d9450, point=...) at /usr/src/debug/kwayland-5.35.0/src/client/plasmashell.cpp:257
No locals.
#2  0x000055555555d6d9 in View::event (this=0x7fffffffdb80, event=0x7fffffffd750) at /usr/src/debug/plasma-workspace-5.10.1/krunner/view.cpp:255
        me = 0x7fffffffd750
        retval = true
        setState = <optimized out>
#3  0x00007ffff519bd9c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /lib64/libQt5Widgets.so.5
No symbol table info available.
#4  0x00007ffff51a33d4 in QApplication::notify(QObject*, QEvent*) () from /lib64/libQt5Widgets.so.5
No symbol table info available.
#5  0x00007ffff46b5b8b in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /lib64/libQt5Core.so.5
No symbol table info available.
#6  0x00007ffff49ebe3a in QGuiApplicationPrivate::processGeometryChangeEvent(QWindowSystemInterfacePrivate::GeometryChangeEvent*) () from /lib64/libQt5Gui.so.5
No symbol table info available.
#7  0x00007ffff49f0c5d in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () from /lib64/libQt5Gui.so.5
No symbol table info available.
#8  0x00007ffff49cf19b in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib64/libQt5Gui.so.5
No symbol table info available.
#9  0x00007fffdedb76c0 in userEventSourceDispatch(_GSource*, int (*)(void*), void*) () from /lib64/libQt5WaylandClient.so.5
No symbol table info available.
#10 0x00007fffeb852277 in g_main_dispatch (context=0x55555583a9b0) at gmain.c:3230
        dispatch = 0x7fffdedb76b0 <userEventSourceDispatch(_GSource*, int (*)(void*), void*)>
        prev_source = 0x0
        was_in_call = 0
        user_data = 0x0
        callback = 0x0
        cb_funcs = 0x0
        cb_data = 0x0
        need_destroy = <optimized out>
        source = 0x55555583c2c0
        current = 0x55555578fba0
        i = 2
#11 g_main_context_dispatch (context=context@entry=0x55555583a9b0) at gmain.c:3895
No locals.
#12 0x00007fffeb852618 in g_main_context_iterate (context=context@entry=0x55555583a9b0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3968
        max_priority = 0
        timeout = 0
        some_ready = 1
        nfds = <optimized out>
        allocated_nfds = 6
        fds = 0x555555a03fa0
#13 0x00007fffeb8526ac in g_main_context_iteration (context=0x55555583a9b0, may_block=1) at gmain.c:4029
        retval = <optimized out>
#14 0x00007ffff4704cef in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib64/libQt5Core.so.5
No symbol table info available.
#15 0x00007ffff46b4b8a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib64/libQt5Core.so.5
No symbol table info available.
#16 0x00007ffff46bc7dc in QCoreApplication::exec() () from /lib64/libQt5Core.so.5
No symbol table info available.
#17 0x000055555555abd1 in main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/plasma-workspace-5.10.1/krunner/main.cpp:92
        app = <incomplete type>
        service = {<QObject> = {<No data fields>}, static staticMetaObject = {d = {superdata = 0x7ffff48e9f60 <QObject::staticMetaObject>, stringdata = 0x7ffff5f0f300 <qt_meta_stringdata_KDBusService>, 
              data = 0x7ffff5f0f1e0 <qt_meta_data_KDBusService>, static_metacall = 0x7ffff5f0cb40 <KDBusService::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, 
              extradata = 0x0}}, d = 0x555555844de0}
        aboutData = {d = 0x555555818040}
        view = {<PlasmaQuick::Dialog> = {<QQuickWindow> = {<QWindow> = {<No data fields>}, static staticMetaObject = {d = {superdata = 0x7ffff4d99800 <QWindow::staticMetaObject>, 
                  stringdata = 0x7ffff6f06ae0 <qt_meta_stringdata_QQuickWindow>, data = 0x7ffff6f06780 <qt_meta_data_QQuickWindow>, 
                  static_metacall = 0x7ffff6d9a520 <QQuickWindow::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}}, <QQmlParserStatus> = {
              _vptr.QQmlParserStatus = 0x5555557615e0 <vtable for View+408>, d = 0x0}, static staticMetaObject = {d = {superdata = 0x7ffff6fc7720 <QQuickWindow::staticMetaObject>, 
                stringdata = 0x7ffff7bc48a0 <qt_meta_stringdata_PlasmaQuick__Dialog>, data = 0x7ffff7bc4580 <qt_meta_data_PlasmaQuick__Dialog>, 
                static_metacall = 0x7ffff7ba3870 <PlasmaQuick::Dialog::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, 
---Type <return> to continue, or q <return> to quit---
                relatedMetaObjects = 0x7ffff7dd2190 <qt_meta_extradata_PlasmaQuick__Dialog>, extradata = 0x0}}, d = 0x555555960220}, static staticMetaObject = {d = {
              superdata = 0x7ffff7dd2160 <PlasmaQuick::Dialog::staticMetaObject>, stringdata = 0x55555555f740 <qt_meta_stringdata_View>, data = 0x55555555f520 <qt_meta_data_View>, 
              static_metacall = 0x55555555e570 <View::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, extradata = 0x0}}, m_customPos = {xp = 0, yp = 0}, 
          m_qmlObj = 0x555555a45ae0
, m_config = {<KConfigBase> = {_vptr.KConfigBase = 0x7ffff5cae480 <vtable for KConfigGroup+16>}, d = {d = 0x5555559fa4d0}}, m_offset = 0.5, m_floating = false, 
          m_history = {<QList<QString>> = {<QListSpecialMethods<QString>> = {<No data fields>}, {p = {static shared_null = {ref = {atomic = {_q_value = {<std::__atomic_base<int>> = {
                            static _S_alignment = 4, _M_i = -1}, <No data fields>}}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, d = 0x555555a4a6f0}, d = 0x555555a4a6f0}}, <No data fields>}, 
          m_plasmaShell = 0x555555a47880, m_plasmaShellSurface = 0x5555559d9450}

I'm no longer able to reproduce, KRunner works again on my Wayland session. Marking as fixed.

Not sure if completely "fixed". Yes it no longer crashes, but in my case now, it goes crazy, it starts poping in and out really fast.

Same issue but different? or a completely new one, not sure.

Yes I can confirm that problem, but I think it's different as it's not a crash any more.