The common problem is that a scanner is suddenly not reading the barcodes at all well and now requires a few attempts to work.
The first thing I would try is to clean the scanner' lens. Scanners today sometimes need cleaning The leading cause is generally people touching the lens so putting fingerprints and dirt on the glass. If so, this problem is easy to fix.
Step 1: Unplug the scanner from everything.
Step 2: Use a wipe sold for optical glasses to wipe the scanner's lens. I do not recommend any standard glass cleaning solution as these often contain chemicals that can damage the lens, e.g. acetone.
Step 3: Now use a dry cloth for spectacles to dry the lens and remove any dirt.
Some scanners can be pulled apart to be cleaned. I do not recommend that you do this. You may damage the unit, which is the last thing you want to do.
If you feel the lens need more cleaning then this, then watch this video.
Now test your scanner.