Had a nightmare situation today at around 3 PM - 3:15 PM.
Was not able to exit even unhedged positions when the margin was at slight negative. Error message was the same which comes when we place fresh orders with less margin than required. Was on a call with Zerodha support around 3:20 PM when magically the situation resolved itself, and I was able to exit the positions, which otherwise would have led to a short settlement / physical delivery nightmare.