This problem happen to a friend of mine, his game pops out the "Server not Responding", and he can't join anyone's server including creating his own.
He is using Windows 10. And have tried several times with the"verify integrity" properties.
Usually we don't have any server problem if he joins my server instead.
Before that (Dont Starve Together, no event), 2 of my friends can create server but none of us can join their server (ping number : ???) except mine.
I assumed because I'm using wired internet connection while my friends using wifi, so I guess it related to it? I'm using Window 8.1.
I guess that's all, Thank you, Klei Devs.