Ive had this before, through wear and tear the BOAB develops slightly rough edges, which the rubber can catch on. You could replace your bucket, but youll probably get the same problem after a while.
The easiest solution that I have found is to identify where on the bucket the rubber is catching, and then superglueing a small piece of old rubber that the rubber in your channel can rest against.
Make sure both your bucket and the piece of rubber are dry before glueing, and use a waterproof glue, otherwise it will fall off in a week.