It seems you shouldn't add the
irh2.TransactionDate in your GROUP BY clause.
You could use MIN() function inside the DATEDIFF function directly.
Try modifying the SELECT and GROUP BY clause like below:
SELECT cir.barcode, irh1.TransactionDate AS Received, MIN(irh1.TransactionDate) AS BeingProcessed, DATEDIFF(DAY,irh1.TransactionDate,MIN(irh1.TransactionDate)) AS DAYS FROM ... WHERE ... GROUP BY cir.barcode,irh1.TransactionDate ORDER BY ...
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