[iOS + il2cpp] the callback of socket's BeginSend sometimes get called few seconds after calling BeginSend

Hi, I think my problem is related to [Asynchronous Sockets still have problem in 4.6.3f1 with IL2CPP] but not the same... I'm using Unity 5.1.3f1 now, and I encountered this problem in iOS + il2cpp mode, if I continuously call BeginSend for around 5~10 times a second, sometimes the "callback" of BeginSend would not response instantly, and will eventually get called after "few seconds", it makes my messages to the client delayed, it works normally in Mono2x mode, so I think it is a bug of Unity/il2cpp, any help?? note: I host server and client in the same device(BeginSend/EndSend and BeginReceive/EndReceive are in the same process), if I had another client(another device) connected to the server, the problem is gone!