Either Screen go black or the desktop from the right screen sometimes goes to the left screen or vice-versa while the other screen is black. Desktop fail to start on black screen. The black screen will display windows fine. Sometimes lots of crashes reported on startup now. Was working OK. Two computers with the same issue here. Logging in, then logging out several times (like 3 to 6 times) eventually seems to make it work. Then everything works perfectly until the next login. If the computer crashes for any reason then it takes longer (more fiddling about) to get it going again. Fedora 23 now. All updates.
As of Wed 23 Dec 2015, latest updates seem to have fixed my issue. So far 3 powerdown cycles, 5 reboots, and mutlple logout and logins, and dual screen with rotation has worked correctly every time. Also KDE seems faster now. Please close.