Sometimes a tiny bit of the sail material along the tape going up in the groove can get pulled into it and bind. You may try to winch it it beyond that point, but that's BAD

!! It's better to pull the sail back down from that point and carefully feed the tape so no sail material gets pinched in. Unfortunately, once this happens the sail becomes "distorted" slightly at that spot, making it likely to happen there again and again, etc. Also, if you do not fix it going up, the sail will not come down easily. This also can be BAD if your furler goes
kaput and you need to get the sail down fast, etc.
Unfurl the sail and sight along the luff up the foil, both sides. You can see where any sail materials has pinched into the groove. That narrow smooth space between the tape rope and the main part of the sail essentially disappears where it is pinched. Use binoculars if necessary.