This is an error code that Bungie is [url=https://www.bungie.net/en/Forums/Post/255429769?sort=0&page=0]currently investigating[/url] but don't currently have a resolution to yet. They know it's a result of having too many "player sessions" opened. This basically means that when you quit Destiny 2, your session for that time played should go away, but this doesn't happen on Xbox. There is not an eta on a fix at this time.