I had something like that happen
On my island my paths use custom designs...
(Which took forever to place btw)
And my friend wanted to tour my island, so I handed him the controllers and talked him through it, the thing is that he hasn't played animal crossing before, so he was pressing random buttons and accidentally removed several parts of my path
It wasn't just in one area either, he kept forgetting what the Y button does and kept removing more of it
As soon as he was done I went back and fixed it.
What did learn from that? Tell your friends how to play before letting them tour your Island.