Sounds like the emulsion is coming off in the presoak. Weird.
Ilford should say in their film docs that a presoak is not required, especially for roll films. When you're doing tray development, a presoak is almost mandatory to ensure that the negatives don't stick to each other.
However, a presoak will not cause the emulsion to come off!
Try a roll without a presoak, and see what happens. If it happens again, then I would suggest that you have a bad batch of film.