I use Logitech USB speakers with my computer. They are set as the default output device as well as the default alert output device.
Just after boot, all works well. All audio plays perfectly. After using the computer for some time, system alert sounds fail to play. All other sounds play perfectly.
This issue is only solved after reconnecting my speakers. I have set my computer to never sleep, so sleep can be ruled out as a cause.
What is causing this and how do I repair it?