getpeername Invalid argument after running a server several times - c

Question

I've got this, taken from beej guide and slightly adapted:
socklen_t len;
struct sockaddr_storage addr;
char ipstr[INET6_ADDRSTRLEN];
char nombreSubscriptor[INET6_ADDRSTRLEN+sizeof(int)];
int port;
len = sizeof(addr);
if(getpeername(fdSocketDevuelto, (struct sockaddr*)&addr, &len)<0){
perror("GETPEERNAME error");
close(fdSocketDevuelto);
exit(1);
}
if (addr.ss_family == AF_INET) {
struct sockaddr_in *s = (struct sockaddr_in *)&addr;
port = ntohs(s->sin_port);
inet_ntop(AF_INET, &s->sin_addr, ipstr, sizeof ipstr);
} else { // AF_INET6
struct sockaddr_in6 *s = (struct sockaddr_in6 *)&addr;
port = ntohs(s->sin6_port);
inet_ntop(AF_INET6, &s->sin6_addr, ipstr, sizeof ipstr);
}
printf("Peer IP address: %s\n", ipstr);
printf("Peer port : %d\n", port);
So I run the client and server and send messages to the server, everything works fine, showing like this
Peer IP address: 127.0.0.1
Peer port : 42639
But if I close and open several times (sometimes it's in the first 1-2 times I try it, but this has happened less), at some point I'm getting this:
GETPEERNAME error: Invalid argument
And before I used the perror and exit(1) in the getpeername I was getting stuff similar to this (it changed slightly in the numbers):
Peer IP address: 2325:2ec7:c37f::
Peer port : 20423
I had already asked here Recv gives Bad file descriptor only sometimes (run the program it works fine, sometimes it does not work) but the question is flat out wrong since it's not the recv that has the failure, it's the getpeername function. And I decided to ask again with proper data this time, which I'm unsure if it's the right thing to do.
The question is: why would this happen? Why sometimes it passes and Ip is fine and sometimes is not? It's two completly different runs of the code, I close and run again, and do not compile or do anything. When it gives me the failure, I wait some minutes (this also looks to be changing from time to time) and I can run again and it works just fine again.