What does the mole mean at ACNL?

Whenever I'm new leaf with my friends in the town of Animal Crossing, after a long time, such a mole comes (I think Resetti). Then there's always that an error has occurred. Why is that? Does the one who owns the city own the Nintendo and that's why everyone in his city goes out? Or does that have something to do with my own Nintendo?

I have not played that for a long time, but I think that turns up when you have not saved the last game. I'm not really sure

I play this very often and I know that happens when…

… You make the wlan or break it off.

… Your friend makes up the game.

… If you have a virus (which is really unlikely).

Would be glad if someone can answer my question that I wrote earlier.

There can be different reasons:

Nintendo of a teammate off (either voluntary or battery empty)
WLAN connection interrupted
WLAN connection interrupted by a teammate
The internet is too slow or crazy and breaks off at some point.

Thank you very much!

Thank you.

Thank you very much!