Running Xubuntu 20.04.
It seems that I am only able to view one open window at a time. That is, when I switch windows (whether by Alt-tab, clicking in the panel, or opening a new window with a keyboard shortcut), all other windows get hidden.
When I Alt-tab, I can see the outline of where the next window will be. If I switch to it, it will appear as expected. But the previous window that was in focus will disappear.
I've also noticed that if I click on (what appears to be) the desktop, but an "open" window is in that space (the outlines of which are shown with Alt-tab, but is hidden because another window has focus), that window will appear. It seems that the windows are still "there", in that they are picked up as a layer between the desktop and the mouse, but they are not visible.
This is very disruptive because it means I can't tile two windows beside each other. Also in-application popups (for example the Find All dialog in IntelliJ) hide the parent window. Most frustratingly, this only started happening a couple days ago.
Thanks!