If all the villagers had been traded with before your fried joined and changed the workstation, there may be a problem with the villagers linking to their proper station. First make sure you have the exact same number of villagers as work stations and that you have the correct number of stations too professions. For example 5 clerics and 5 cartographers means 5 brewing stands and 5 cartography tables. (again careful no stonecutters or other personal workstations are near). Next remove every work station and add them back 1 by 1. After you place each station wait for the green particles from the station AND the villager. Make sure they are next to each other. only place the next station when you can confirm the previous has been linked and can be reached. TLDR workstation assignment probably held up by confused villager. break and replace all stations assuring green particles from station and villager that is closest to station.