In contrast to X the window misses a title. Reproducible: Always
Reassigning to systemsettings - looks like systemsettings is not setting any title. As soon as one changes to a module the title gets updated.
Just adding: this is on Wayland.
Upstream bug report: https://bugreports.qt.io/browse/QTBUG-56475
And code review: https://codereview.qt-project.org/#/c/173514/