The bungie set-up is something you have to experiment with to see what works best. On our Hobie 18, the bungies were attached at the bottom of the diamond wires on the mast. A bungie went down to the port and starboard outboard ends of the dolphin striker. We also experimented with them halfway in on each side of the dolphin striker and very close in toward the mast on each side. I can't remember now which location seemed to work best.
Do you have pigtails on your jib clew, with the jib sheet turning blocks on the ends of the pigtail? I found that when we used a pigtail, the longer the pigtail, the more problems I had with the jib sheet hanging up on something. On the other hand, some people love the pigtail.
Are you tacking the jib properly? When you tack, the crew needs to keep some tension on the old sheet all the way through the tack, while at the same time bringing in the new sheet without allowing slack in that one, either. Otherwise, you have sheets just flailing and flying around up there, and they will catch on anything they can find.
I don't know whether the Hobie 21 has a mast rotator bar on the inboard side of the mast. If so, that was the major hangup for the Hobie 18. As crew, I always waited until the mast rotated before completely releasing the former burdened sheet, because otherwise, it would catch on that rotator bar every time.
