To my knowledge this bug has existed in the Xbox version of Stardew Valley at least since I started playing in July 2017. When I first bought the game I had internet problems and thus played offline. When I reconnected to online, all of the achievements I had technically completed would not unlock. These are the achievements that did not unlock while I was offline: A New Friend Reach a 5-heart friend level with someone. Treasure Trove Donate 40 different items to the museum. Gofer Complete 10 'Help Wanted' requests. Moving Up Upgrade your house. Cowpoke Earn 50,000g. Ol' Mariner Catch 24 different fish. When I got various other achievements related to these, such as earning Homesteader (Earn 250,000g), it did not unlock Cowpoke (Earn 50,000g). However, when I started a new game and then completed these things again, they unlocked. Now, playing my original character that I had been offline with, I finally finished the museum collection, but I can unlock neither A Complete Collection (Complete the museum collection.) or Mystery Of The Stardrops (Find every stardrop.) because I had donated some of the items while I had been offline. Usually Xbox games will save what the player accomplishes while offline and then when you go online it'll reread your accomplishments and unlocks the appropriate achievements. My concern is that at no point does Stardew Valley recheck if tasks have already been completed; whatever you accomplish while offline simply goes into the ether. Thank you for your time. *Edits: General rephrasing.