Quoted from frenchmarky:

Also check the 1 point score reel's match number wiper switch, the outer wiper should be pointing between '4' and '5'. Someone might have accidentally reinstalled it incorrectly. It can be placed in 5 different positions on the reel hub so if it's wrong, when you score a match the reel and match numbers will always be 'off' by a given number. Difficult to see how the match unit reassembly would have caused this since the wipers only install in one position.