A very similar situation - we called it the "million rand" muffin problem and one store kept getting occasional misreads on barcodes where the price was embedde

A very similar situation - we called it the "million rand" muffin problem and one store kept getting occasional misreads on barcodes where the price was embedded in the barcode. We looked at our code and were rather stumped - a simple ACK/NAK serial RS232 protocol - replaced serial boards. I got sent onsite (my fate as lead programmer) and sat in the office and waited - hours later it happened and when I looked at the offending muffin I looked down and noticed the barcode scanner was from another manufacturer (cheaper) we normally did not use. I send some samples to manufacturer - few days later - turned out it was firmware issue.