What's the problem with my map positioning

I made a map positioning app, following is my design: when user logined, his position will be showed on the map automatically, and his location is in the center of the map(which means the blue point is in the center of map). But when i logined in my iphone5s, the blue point always isn't in the center of map, there's a offset in my phone. But the situation is normal in others iphone6, when he logined, the blue point is in the center of map(his position shows in the center of map). Why it has an offset in my phone?