Edit added: 15 Feb 22. Finally bought a new Fitbit Charge 4. Same sleep data issue plus some. Of course the issues always start occurring just after the warranty ends. What a piece of junk...certainly not worth the purchase price. I will not be purchasing another Fitbit. I'm also going to notify Sam's Club, which is where I bought both. Original rating 2/21: Sleep score does not work consistently, even when enough hours should be logged (generally 6.5-8 hours). Very aggravating.