Exactly the same issue in the cleanboot state. I had to keep the start10 service enabled, but i disabled all other non-windows services and startup items. The start10 menu is still scaled incorrectly on the 1080p monitor as in the previous screnshot.
Also another issue I noticed while trying out the cleanboot state. Not only is the visual scaling incorrect, but I can not select any of the start menu items after about halfway down the menu.
Print screen does not capture my mouse cursor, but in this screenshot i am selecting "Resource Montior"
In this screenshot I am trying to select "Services", everything after the "Resource Monitor" will not respond to selection, a similar thing happens to all the start10 menus on this 1080p monitor. ie. Universal Applications, Personal Folder, all stop selecting about halfway down the menu.