Offline Friends/Cannot Connect

This happens every time I try to play Smash with my friends on my 3DS: it shows that they are offline. Sometimes I host a room for them and they tell me they cannot connect.

As far as I know, I don't need an update because I'd assume it'd try to update when I put my game in.

A friend of mine just updated his game and it says he was online, and when it finished it now says he is offline.

I have always had this issue and have never found a fix. Can someone please help me?

EDIT We can see each other online now; one says "online" and another has a room, but we're all getting error code 018-0515. One is using wifi at a library or McDonald's sometimes to play but we've been able to connect before. She has no home internet.