Comment 39 for bug 1769383

The above stack trace seems to be tied to this other message:

Nov 16 11:41:38 scruffy gnome-shell[5626]: Object Meta.WindowActor (0x560d5092bb00), has been already deallocated — impossible to access it. This might be caused by the object having been destroyed from C code using something such as destroy(), dispose(), or remove() vfuncs.

The error seems to be on the disconnect() call in Transparency.disable():

        for (let key of this._trackedWindows.keys())
            this._trackedWindows.get(key).forEach(id => {
                key.disconnect(id);
            });
        this._trackedWindows.clear();

Presumably the remainder of the clean-up performed by this function and its callers is not performed, leaving the shell in an inconsistent state.

I'm still not sure why gnome-shell is trying to disable the extension. Does it disable extensions when locking the screen?