select view->show hidden devices. When those two com ports show up

Tried that. They didn't show up. Couldn't delete them.

In the end, I just reassigned the device to COM3, and then removed it. This appears to have marked COM3 as unused, so the next time I installed it, it took COM3 without complaining.

I'll have to do something equally cunning to mark COM4 as unused if I need to use it in future.