Check for fabric caught in the closed zipper teeth and gently pull it out using a pair of tweezers. If no fabric is visible, rub a light coating of graphite pencil, vaseline, a crayon/candle ...

After cutting off the fuzzies ... do is sew a few stitches across the end of the teeth and then sew the tape back to the bag. Got a broken zipper box? You can fix that with 3D printing.