Comment 76 for bug 362359

I just experienced this behavior with Ubuntu 20.04 (Gnome, X11, Nvidia GTX 1070). Only one window had focus. Some windows appeared in front of the focused window, but I could not click on them - clicking on them only sent mouse clicks to the window in the background. The "dots" in the dock that show what applications are open all disappeared, and if I moved my mouse over the apps then they became highlighted and wouldn't un-highlight. This is the first time I've experienced this issue, I've been using Ubuntu 20.04 since release, and 18.04 before that since its release.