More Fed tax owed...

So my Federal return was accepted and processed in January. Last week I got a letter from the IRS saying that I had omitted reporting some federal stimulus $, but I had entered all the information correctly. Did Turbotax change an algorithm - or - did the Fed's change their stimulus payment tax status? It's almost a $1400 increase! Wouldn't the Turbotax software catch this?

 

Any suggestions or insight would be greatly appreciated!