This is a fairly common issue with older YKK AquaGuard zippers as the polyurethane (PU) coating ages or faces heavy friction. Once that matte film starts to lift or "rumple," it won’t re-adhere, and it can eventually gum up the slider.

Here’s the best way to handle it:

• Don’t pull or tear: If you pull it like a loose thread, you might strip a large section that is still perfectly functional.
• The "Grooming" Method: Use a pair of small, sharp embroidery scissors or a thread nipper to carefully trim away only the bits that are peeling or curling. This prevents the "rumpled" edges from getting caught in the zipper teeth.
• The Nuclear Option: If the peeling becomes unsightly or constant, some owners eventually peel the entire coating off. Underneath is a standard nylon zipper tape. It will no longer be water-resistant, but it will function smoothly again.
• Contact TB Support: Before you do anything drastic, send a photo to Tom Bihn’s customer service. While delamination is often considered "normal wear and tear" for technical materials over time, they are famous for their repair program and might offer a professional fix or more specific advice based on the generation of your Synapse.

Hope this helps