Hi! Thanks for reporting this. If you have already completed Mesmerize and are trying to rerun this mission in a Fireteam, there is currently a [url=https://help.bungie.net/hc/en-us/articles/27062192032404-Destiny-2-Year-7-Known-Issues-and-Vital-Information]known issue[/url] where some players are unable to launch into the mission with other players if they have already completed it. We are actively investigating this issue and appreciate your patience while we work on this! [quote]Players who have already completed unique missions in the Episode: Echoes story will not be able to launch into them again with other players who have not completed them yet.[/quote]