I notice quite a few of these lines when looking at journalctl, so I thought it
might be an indication of a problam which needs fixing:


kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 1105,
resource id: 35651588, major code: 18 (ChangeProperty), minor code: 0
kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 3032,
resource id: 29360133, major code: 2 (ChangeWindowAttributes), minor code: 0
kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 4165,
resource id: 6291470, major code: 2 (ChangeWindowAttributes), minor code: 0
kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 4170,
resource id: 6291483, major code: 18 (ChangeProperty), minor code: 0
[...]
kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 5400,
resource id: 46137348, major code: 18 (ChangeProperty), minor code: 0
kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 6149,
resource id: 46137344, major code: 18 (ChangeProperty), minor code: 0
kwin_x11[3140]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 6153,
resource id: 46137345, major code: 18 (ChangeProperty), minor code: 0
[...]
plasmashell[3145]: QXcbConnection: XCB error: 2 (BadValue), sequence: 3480,
resource id: 46137350, major code: 142 (Unknown), minor code: 3