I'm running Ubuntu 16.04. I made the mistake of apt-get installing kubuntu-desktop, and removing it. I've solved all visible problems, apart from a missing icon in the top right panel. This is similar to the issue mentioned in Strange icon in Unity top menu bar after installing KDE . The icon I'm seeing is the one with the red-circle-in-the-box thing. I've tried the steps mentioned, and also tried to figure out which app is causing it by turning off things via unity tweak tool... and it appears it's not a built in one. If I click the weird icon, I get a pop up menu, but with no entries. Is there a way to figure out which application the icon is for? Is there a list somewhere?
I even reinstalled ubuntu-desktop, but to no avail.