The reason you may have it and they don't could be specific connection issues to the server. Have them check the actual app through the Xbox to see if it says update. If not uninstall/reinstall to see if that pushes the update through. ^TK
Have you tried to go directly to the app in your Xbox Games to see if it will update through force? If not, uninstall/reinstalling may be a good idea if you don't have any single player worlds you don't want to lose. ^TK
If you don't have any single players Worlds you're fond of please uninstall the client and reinstall it on your Switch. Let me know how that goes for you! ^TK