I need some help figuring this out.

ALT-TAB stopped completely to work. It was happening 2/3 of time and a logout/reboot used to solved it.
Changing the shortcut to CTRL-TAB works fine in the TASK SWITCHER. I use it as the ALTERNATIVE.
I have searched every shortcut configuration in the SYSTEM SETTING to find some conflicting ALT-TAB.

I do have extra keyboards (it a notebook) for places where I use it (as I had when it worked).

Any help is appreciatted.

I am using KUBUNTU 18.10 - PLASMA 5.14.4 - QT 5.11.1- kf5 18.04.3

-rsd