I’m still experiencing it with Brave and Thunderbird.
Doesn’t seem to happen with Firefox, though
Nov 14 20:12:55 Y4M1-II systemd[9205]: Started snap.thunderbird.thunderbird-218c47bb-9cdf-4585-8487-1e76547933b3.scope.
Nov 14 20:12:55 Y4M1-II systemd[9205]: Started app-thunderbird_thunderbird-4758a597c99d427f91814da5b05c365a.scope - Thunderbird Mail - Mail Client.
Nov 14 20:12:55 Y4M1-II plasmashell[133984]: /user.slice/user-1000.slice/user@1000.service/app.slice/app-thunderbird_thunderbird-4758a597c99d427f91814da5b05c365a.scope is not a snap cgroup
Nov 14 20:18:39 systemd[9205]: Started snap.brave.brave-0149a21f-9f53-4774-9189-d26c3e467622.scope.
Nov 14 20:18:39 systemd[9205]: Started app-brave_brave-ef45525cece44fb8aec48a679c000d9d.scope - Brave Web Browser - Web Browser.
Nov 14 20:18:39 kwin_x11[9529]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 9515, resource id: 33557375, major code: 18 (ChangeProperty), minor code: 0
Nov 14 20:18:39 plasmashell[136250]: /user.slice/user-1000.slice/user@1000.service/app.slice/app-brave_brave-ef45525cece44fb8aec48a679c000d9d.scope is not a snap cgroup
Nov 14 20:18:39 kwin_x11[9529]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 9550, resource id: 33557376, major code: 18 (ChangeProperty), minor code: 0