hI upgraded to KDE plasma 5.5.5 following the KDE 4.11 Gentoo wiki page:
sddm works fine, I can start a working openbox session with it. (Yes sddm is in the video group)
However, when I start plasma, I get a dark screen with working a mouse and a limited krunner.
I have an extensive xorg logfile: http://pastebin.com/m0mHVXJq
I extracted some relevant lines from it:
QCoreApplication::arguments: Please instantiate the QApplication object first QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave. kscreen: Failed to request backend: unknown error
I use openrc and a Nvidia GeForce GTX 760 with 361.28 driver version with 3 displays but two xscreens.