Overwatch can be played with overclocked hardware, but none of Blizzard’s games offer official support for it (more info here). Your GPU is not responding to Windows fast enough, so I’m thinking this is related to the overclocking. It’s possible that the card is not performing at it’s best anymore, or that there is an issue with the supply of power it is receiving.
This often interferes with Overwatch, so I’d recommend disabling the Steam Web Helper utility.
Manually check for Windows updates. There was a new patch yesterday that specifically addresses how GPUs interact with Windows.