I'm having a similar issue, but not quite the same. The display works fine upon booting up (Kubuntu 15.10 beta 2), but if I let it go to sleep (or turn off the TV I use as a monitor) and return, then I get no display, and have to reset the computer to get a display back.
Just yesterday something changed (been installing upgrades like crazy, being a brand new PC on beta 2), and the display now works when I wake the computer, but I cannot get back into my established session (although I can start a new one).
I'm using SDDM to login, KWin as my WM (with Plasma 5.4 as my DE); I'm honestly not sure what logs I could provide to aid this bug, but if somebody else knows I'll gladly spew any output from my system that can help!
I'm having a similar issue, but not quite the same. The display works fine upon booting up (Kubuntu 15.10 beta 2), but if I let it go to sleep (or turn off the TV I use as a monitor) and return, then I get no display, and have to reset the computer to get a display back.
Just yesterday something changed (been installing upgrades like crazy, being a brand new PC on beta 2), and the display now works when I wake the computer, but I cannot get back into my established session (although I can start a new one).
I'm using SDDM to login, KWin as my WM (with Plasma 5.4 as my DE); I'm honestly not sure what logs I could provide to aid this bug, but if somebody else knows I'll gladly spew any output from my system that can help!