I was tabbing between rounds while looking at builds. I tabbed back into the match just before the purchase time. Instead of being presented with the hero menu, I was in game and observing my character as normal. I tried my keybinding to access the menu and it did not work. I opened controls, confirmed the binding was still the same, rebound it to the same button it was, and attempted to pull it up once again. It failed. Shortly after the clock ran out for making purchases.