Might be rubbing against the side plate of one of the blocks in the system, like the block at the masthead. If it rubs on the side plate that can force the braid of the line to distort over time and cause twisting. If its happened with multiple halyards this might be the issue. Harken micro at the masthead? Try a block with plastic side plates instead, the micro has relatively sharp stainless edges that can do this. Might also not have enough travel on the athwartship strop at the masthead which would cause rubbing on the side plate.