There are several possible reasons for your problems. Any special reason you are using brass rather than silver? I've not soldered brass with silver solder - Judy Bjorkman, can you comment?
In my experience, silver solder works fine with brass. Obviously it’s
not a great color match. As I’ve mentioned before, I used bits of
hammered brazing rod as a solder for brass (only if it’s red brass,
which has a higher melting point). It’s quite a good color match. Rio
and IJS have solders which are yellowish and fairly suitable, at
least better in color than silver solder.
I don’t remember the original project description. Have you ever
tried fusing the brass links (if they’re not too heavy)? Sometimes I
can get that to go quite well! (Other times, not.) But pick
soldering is the most dependable. I have no advice to offer on that,
beyond what other folks have already said.
Judy Bjorkman