I had the same problem. The app crashed at about 1600 MKPolylines, then I was able to reduce them to <10 (each with lot more points) and for now seems OK. (The Metal assertion still fails and the memory usage grows to 1G but then reduces itself to the normal 200M.)

I also had this problem, got a crash at about 1600 MKPolylines. Then I reduced them to < 10, each having lot more points and for now seems OK. (The Metal assertion still shows, the memory grows to 1G but then reduces itself to the normal state about 200M).