This is caused by the lack of either playerprofiles8.lsf or LevelCache folder in the %appdata% folder, which contain records of your character in the world. Not sure which one exactly, most likely the profile one, but these are not uploaded to the cloud. So if you reinstall Windows or in your case move to another system then these files do not transfer over.

The symptoms of this issue is that all of the world's records regarding your character become reset, so certain things that you did with your character and locations that you visited are now treated as if you never have before. It's also why you gained a 2nd chest which is now considered yours because your character is being treated as a different character, despite being exactly the same one. Same character, but blank state basically.

If you still have access to your Windows PC then copy-paste the entire Baldur's Gate 3 folder from the %appdata% location and then reload a save before you gained the 2nd chest.

[Linked Image from bg3.wiki] Minthara's Compendium Of Issues