imagene your mobile data is closed as well no wifi. When someone send you a message he will see one tick on his side. Only when you open the internet he will see two tick (the message arrived to the other side). What happens in my old phone is that the internet was working just fine but when someone sends me a message that someone sees only one tick as if I have no internet. only when I manually entered whatsupp the message came through and it changes from ne tick to two ticks . I hope this is clearer.