Slow startup of Plasma 5.5 in Kubuntu 16.04

Question

My recent Notebook (Intel i3-6100 with SSD) boots from BIOS to the login of SDDM within 8s. After entering my credentials it takes 31s (no matter if I have autostart of Firefox and Thunderbird). While waiting these 31s the blue progression bar shows "100%" after very few seconds but stays the rest of the time at "100%".

If I reset my Plasma/KDE configuration it only takes few seconds as it was in Kubuntu 15.10 partly with NEON packages. My Plasma configuration is very basic with no bluetooth. There are no errors in ~/.xsession-errors and if I monitor the startup of Plasma with htop I see no activity. After the slow startup everything is fast.

The output of systemd-analyze blame is:

5.889s NetworkManager-wait-online.service  
3.817s apt-daily.service  
2.520s swapspace.service  
568ms dev-sda1.device  
224ms accounts-daemon.service  
...

Do you have an idea or how I can better monitor the cause of the slow startup of Plasma?

Solution

There is a workaround to avoid this problems: "disable the splash screen (System Settings -> Workspace Theme -> Splash Screen -> Set Theme to "None")" (see https://bugs.launchpad.net/ubuntu/+source/breeze/+bug/1584604/comments/14). The bug seems to caused by breeze.