I got that when I installed using the live KDE media. Before that, there was an error in the final stage of install (following the reboot). I did not write down the message.
I reinstalled using the DVD image. I do not have that problem with the install from DVD image. (In all cases, I actually used a USB device for the install).
As best I can tell (and I am partly guessing), what used to be done in the final stages of install, following the reboot, has been moved to the earlier stages before the reboot. However, the live media still depends on that now non-existent final stage following the reboot. I’m assuming this will be fixed for M1 (milestone 1). And we still do not have a schedule for milestone releases.