Aaaah, the joys of poo bracelets. :lol:
When bunnies moult, they'll ingest more hair and this comes out with the poo, stringing them together. I always take it as a good sign - far better for the hair to be working its way right through than to be causing a blockage.
It can help to make sure they're drinking plenty (mine prefer slightly warm water so I refill their bowl several times a day).