Comment 58 for bug 1573408

Possibly same bug:

Upgraded from 14.04LTS to 16.04LTS. Had to remove ROS and disable third-party repositories.

After the upgrade, the Ubuntu Software application showed the third-party repositories as disabled. Re-enabled them.

The Ubuntu Software store would not show ROS or KiCAD from third party repositories, although it would show "Kicad Snap" from Canonical's store. The repositories used are

They repositories are validly added; doing

    sudo apt install kicad

installed KiCAD OK. So it's just the GUI program that's broken. It just shows Canonical stuff.
Even with kicad installed and working, it doesn't show up in the Installed tab.

(Or is there now some secret hidden checkbox or option you have to enable for third-party
packages to work right?)