This has happened to me 3 times today, it appears to happen randomly, as it has happened to me once before 2 days ago. I can't select anything, I can't move any units.
There's no way to bring up any menu, as it's aprt of the hud. This has happened on both Fullscreen and windowed mode (It happened before whilst I was playing Galactic War in fullscreen, I went to Windowed hoping it would fix it) And the only way I've found to fix it is rebooting the game. Wherever I move the mouse the planet moves with like I've got middle mouse held down. As I select something my hud just disappears and I'm left with this.
In the middle of a co-op game with a friend fighting a bot.