SUMMARY
PagerModel from Pager applet is crashing Latte and probably Plasma on exit.


STEPS TO REPRODUCE
1. Open Latte under wayland environment
2. Add a Plasma Pager applet in Latte by drag n' drop from Widgets Explorer
3. Close Latte, fastest way is (Meta+W and afterwards follow Ctrl+Q)

FINDINGS FROM INVESTIGATION
A. Latte git version provides an option for the user to cycle between VirtualDesktops and Activities when the user uses the mouse wheel on empty areas of the Latte Panel. In order to change VDs and Activities Latte is using the PagerModel as observed at file: https://phabricator.kde.org/source/latte-dock/browse/master/containment/package/contents/ui/layouts/loaders/Pager.qml . Same crash occurs when this Latte feature is enabled

B. From testing out the crashes it is pretty clear that even if the Pager applet is removed from the user and afterwards we try to close Latte, the same crash occurs. So probably the PlasmaWindowManagement used from Pager is not cleared correctly on exit... Please note also that this crash does not occur for plasma taskmanagers OR features that are using the TasksModel from plasma-workspace which is probably doing something better in order to release the PlasmaWindowManagement used by it.

OBSERVED RESULT
crash for Latte

EXPECTED RESULT
not crash

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: OpenSUSE TumbleWeed
KDE Plasma Version: 5.15.5
KDE Frameworks Version: 5.57.0
Qt Version: 5.12.3

ADDITIONAL INFORMATION
Crash report:
[KCrash Handler]
#5  0x00007ffb536dcf19 in  () at /usr/lib64/libwayland-client.so.0
#6  0x00007ffb536d8cf1 in wl_proxy_destroy () at /usr/lib64/libwayland-client.so.0
#7  0x00007ffb568ae677 in KWayland::Client::PlasmaWindow::release() () at /usr/lib64/libKF5WaylandClient.so.5
#8  0x00007ffb568ae69a in KWayland::Client::PlasmaWindow::~PlasmaWindow() () at /usr/lib64/libKF5WaylandClient.so.5
#9  0x00007ffb568ae7c9 in KWayland::Client::PlasmaWindow::~PlasmaWindow() () at /usr/lib64/libKF5WaylandClient.so.5
#10 0x00007ffb5429a17b in QObjectPrivate::deleteChildren() () at /usr/lib64/libQt5Core.so.5
#11 0x00007ffb542a2df4 in QObject::~QObject() () at /usr/lib64/libQt5Core.so.5
#12 0x00007ffb568aef29 in KWayland::Client::PlasmaWindowManagement::~PlasmaWindowManagement() () at /usr/lib64/libKF5WaylandClient.so.5
#13 0x00007ffb5429a17b in QObjectPrivate::deleteChildren() () at /usr/lib64/libQt5Core.so.5
#14 0x00007ffb542a2df4 in QObject::~QObject() () at /usr/lib64/libQt5Core.so.5
#15 0x00007ffb4f8fa923 in  () at /usr/lib64/qt5/plugins/kf5/org.kde.kwindowsystem.platforms/KF5WindowSystemKWaylandPlugin.so
#16 0x00007ffb53b2e42c in __run_exit_handlers () at /lib64/libc.so.6
#17 0x00007ffb53b2e55c in  () at /lib64/libc.so.6
#18 0x00007ffb53b16b82 in __libc_start_main () at /lib64/libc.so.6
#19 0x00000000004695aa in _start () at ../sysdeps/x86_64/start.S:120
[Inferior 1 (process 31749) detached]