Hi - did you find a solution to this? I'm having the same problem and I've tried every combination of male/female, adult/teen, adult/adult etc, and nothing works.
Like you say, when you go back once the Sims have completed the task, there's no exclamation bubble to click like with any other hobby, they just complete the task, levelling up. But there's no collectible to collect!
It's very frustrating.
I just tried it again, seeing as there was an update, and it's doing the same thing. No matter what I do, if I am not there at the precise instant their hobby finishes or spend LP on it (which never happens), I get no reward. Yet, they continue to level up.
It's particularly annoying because half of my mall is completely blocked and I cannot continue to build it because I need to collect the items from this hobby to unlock several stores, so it's just laying there completely useless.
I still haven't found a solution nor anyone besides you with this problem, but it's annoying the hell out of me.
