What barcode symbology is being used on the labels? A lot of barcodes have a check digit at the end... It's a calculation of all the numbers before it, so it cannot just be any number. And when transposing batches of data from 1 place to another, some formatting can get lost, or misrepresented.

Select a random product, and go to its item page on your device. Use the barcode scanner to scan the barcode into the item's SKU field... Now look at that item in your Item Library and notice it's SKU as entered exactly by your scanner. Compare it to the exact digits that were assigned to it when you were editing it in Excel. You will probably notice that there is a 1 number difference... No?