"Apple did not say what causes the cracking, or if a fix is planned. Affected users have been able to get in-store replacements, though with limited stock available, some are having to wait.

According to Apple, the problem is limited in scope. Most users are not going to see an issue with their ‌iPhone Duo‌ display, and it's not a defect people have to worry about showing up over time. On affected units, the crack seems to show up shortly after purchase. "