Constantly locating server

Whenever I try to join my friend's multiplayer world, it doesn't start because it says it's locating the server. I played on it before working fine and I have done everything. I restarted my pc, reinstalled minecraft and my friend restarted the server but it isn't working.

 

Edit: It's something wrong with the world because we went on another world together and it worked but when we copied the world I couldn't join it.