Dual Application Switchers
I have a dual monitor set up running Ubuntu 16. The goofy thing was there were two application switchers. One would be displayed on the monitor with the active window and the other would be displayed on the monitor with the cursor. If the cursor was on the same monitor as the active window, one would be on top of the other and it was difficult to tell what application would become active.
To fix this, run CompizConfig Settings Manager and uncheck “Application Switcher” in the Window Management section.