I thought faulty line too.
When you tie the blood knot you twist it 5 or 6 times and put the tail back through the loop near the hook, yes? then as you pull it down another loop it formed at the other end of the knot, put the tail back thru that loop , pull it all down tight and you will never have a knot pull out. I tie the same knot whether it be fluro, braid or mono. I even tie that knot with wire.
I was having trouble with the running sinker rubbing on the braid and fraying it so i was doing the same as you, braid- swiv-mono with sinker-swiv-leader-hook but i dont really like having so many joins, more places for something to go wrong. After say ten or so cast cut 6in off the braid and tie again.
But i really think it sound like the braid might be dodgy. And when your fishing in that rocky, pilon sort of territory, lock it all up tight. You cant afford to let jack run an inch or they will have you before you know it.