Did you probe this membrane yet? If so, how do the bands look? If this happens again, I would recommend also doing a ponceau stain before blocking to see if the rest of the membrane also has issues. What are you using as your transfer system (wet or dry)? If wet, I would recommend getting new sponges. We had a similar issue years ago and our sponges were old and it was affecting the electrical current of the transfer.
During transfer keep the transfer sandwich and the assembly in cold room or in cold temperature. High temperature are often encountered when gel transfer is carried out at RT like you did and may result in such observations. additionally, keep the cool packs in your transfer assembly.