Hi, on an up to date manjaro machine I am starting to see this.
In some occasions plasma starts up broken. After the login, you get the bottom panel, with all the widget working, but the desktop area itself remains black (without its icons and wall paper) and unresponsive (right clicking in it with the mouse does not offer a contextual menu).
In this state, pressing F2 opens the runner, but in the wrong place (right aligned rather than centered).
The weird thing is that if you issue a
plasmashell --replace everything is fixed.
At this point the next login may be fine, … or again not … etc.
Looks very much like a race. Any idea?