Cannot switch between windows of the same application

This was my problem too. Alt+<key above tab> didn't work to switch windows in the current application.

In addition, when i pressed and held down the super key to see the unity shortcuts, normally one would see this:

I'm assuming that is for a US keyboard? I stole the screenshot from another post, and on my danish keyboard it now shows Alt + Onehalf.

But when I had this problem, I did not see the line pointed to by the red arrow!!!

So check if you see a keyboard shortcut for "Switch windows of current application". If you don't this is for you:

The fix was as hinted at above to change the XKBMODEL setting in /etc/default/keyboard where I changed from XKBMODEL="microsoft4000" to XKBMODEL="pc105".

I did that and ran sudo dpkg-reconfigure keyboard-configuration. Not sure this last step was required.

Then I needed to reboot.

Now it works.

Suboptimal, but you can use the down arrow after Alt + Tab.

You can change the short cut key of "switching windows" to Alt +Tab. Then you will be able switch between windows (not applications)

Exclusive for ubuntu 18.04 LTS - search keeyboard in settings and do the above change