1. Start a Classic Game with a timer
  2. Wait until slightly after the timer hits 0:01, and press Guess or hit the spacebar with a guess down
  3. The error in the attached image pops up, and you are forced to refresh the page (by hitting Try Again)
Confirmed on an incognito Google window with no browser extensions.
The following response is observed in the Network tab:
{"error":"GameError/InvalidState","message":"InvalidState"}