I would be miffed too If I had 4.9 showing for cleanliness when I had proof that guests had only given me 5*. I would however double check each individual scoring per guest for that listing before contacting customer service to make sure that one guest hadn't marked you down and had gone unnoticed.
Have you checked every individual rating as Joelle suggested? If yes an no reason was found for this 4.9, did you try reaching out to the Support team yet?