It may be that a bug report is required, but FWIW I did find the following threads which discuss possible workarounds that may be worth investigating...
I just reinstalled kde-print-manager, rebooted - and plasma crashed again with the same behavior. I then removed it again, rebooted - and everything...
If your UEFI is still set to "Hybrid Graphics" and you are still after step 6 (of the Bumblebee instructions you refer to) without a graphical login...
Glad to be of help. I feel I must add that KDE as it is now is not as clear as it was in 3.5 about it's locality settings. People have e.g. problems...