Running a wayland session, I have the menubar style set to "title bar button", and when I click on the button, the menu shows up somewhere far away from the button on my 1080p 15.6" monitor.
The menu is rendered by kded5 and not by kwin or the application, we currently have no way to have external applications align/position themselves with other windows.
*** Bug 391648 has been marked as a duplicate of this bug. ***
*** This bug has been marked as a duplicate of bug 430662 ***