Hi Akramullak,
On which branch do you arrive systematically ?
Please may you add a Javascript activity after the Preloading activity, and writes down a logInfo("[Unsubscribe webApp] Business Unit" + recipient.@BU);
then check web.log for result (on MTA / web server, not applicative server).
Or more convenient, use the debug mode in preview window pane, with a specific test user account, so you can see the context (ctx) content and understand better.
Regards
J-Serge