Slowdown and lost windows when connecting/disconnecting external monitor
In the Display settings, under the &quot;Arrangement&quot; tab, I had previously dragged the menubar to the external monitor. This had some benefits, such as causing the Application Switcher to appear on the external monitor, which is the one I was usually looking at. However, moving the menubar back to the built-in monitor eliminated the problems I was having. There is now no slowdown when connecting, and when disconnecting windows reallocate themselves between monitors as expected.