Bug 376659

I‘m completely new to Linux, if you need any additional information please explain how I can get it :)

Problem: Discover does not show any software, it is completely empty.

What I did:
I installed Kubuntu using an usb stick with kubuntu-16.04.1-desktop-amd64.iso parallel to Windows 7 (partitions „/“, „/home“ and „/swap“ manually created), system language „German“. 
After installation discover _did show_ software in its categories (I could browse them). Search function however _did not work_, it just showed no results no matter what I entered.
System said there where around 230 updates available which I installed. After installation of these updates discovery is empty. No software is shown in categories any more, and search function still does not work. Discover only promotes some software in the rotating top area (VLC for example) – those descriptions float out of their boxes. If I click on one of these promoted software a detail window with description and install button appears. 
Since I‘m new to Linux I tried 16.04 Ubuntu (with unity) and then Ubuntu MATE on the same machine. Both had a fully working software center. So I believe this is a bug in discover.
Maybe related to
https://bugs.kde.org/show_bug.cgi?id=372729
https://bugs.kde.org/show_bug.cgi?id=367526
https://bugs.kde.org/show_bug.cgi?id=363392
https://bugs.kde.org/show_bug.cgi?id=376241
https://answers.launchpad.net/ubuntu/+source/plasma-discover/+question/294053
https://bugs.launchpad.net/ubuntu/+source/plasma-discover/+bug/1573994