It also happens on me and it so annoying why there are such bounties that do not give rewards to the participants even they accomplished their tasks. Because of that I learned a lesson not to join bounties which had a bad conduct from the public.
Every new bounty hunters will get this experience, soon or late, haha. In the first time, none of us know how to choose a good bounty to do, we just do it because we think "oh, this campaign is good, big reward pool, limited participants, ..."