UDP broadcast being sent, but not received (yes, again) - sockets

Question

I have a question seemingly the same as this one, yet having checked that and others I can't see the difference.
I have an app that receives UDP broadcasts. It loops back on itself properly, and can on the same machine receive from another app. However, when I try to receive from an external GoPro Hero4 Black,
I can send and receive TCP with the camera within the same app
Another app on the same machine can receive the UDP broadcasts from the camera
This app sees nothing
I checked for properly using INADDR_ANY, and it's being done in the code. Given the machine does receive the packets, and the app itself can do TCP with the camera, the error has to be in the UDP receive code, yet that works between apps on the same machine.
Question: What could cause this behavior?
My belief is the problem is in my understanding of UDP broadcast receive, but nevertheless, in response to a comment, here's code. This initializes the receiver:
int yudpsocket_server(const char *addr,int port) {
//create socket
int socketfd=socket(AF_INET, SOCK_DGRAM, 0);
int reuseon = 1;
int r = -1;
//bind
struct sockaddr_in serv_addr;
serv_addr.sin_len = sizeof(struct sockaddr_in);
serv_addr.sin_family = AF_INET;
if (addr == NULL || strlen(addr) == 0 || strcmp(addr, BROADCAST_IP) == 0) {
r = setsockopt( socketfd, SOL_SOCKET, SO_BROADCAST, &reuseon, sizeof(reuseon) );
serv_addr.sin_port = htons(port);
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
} else {
r = setsockopt( socketfd, SOL_SOCKET, SO_REUSEADDR, &reuseon, sizeof(reuseon) );
serv_addr.sin_addr.s_addr = inet_addr(addr);
serv_addr.sin_port = htons(port);
memset( &serv_addr, '\0', sizeof(serv_addr));
}
if (r == -1) {
return -1;
}
r = bind(socketfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));
if (r==0) {
return socketfd;
} else {
return -1;
}
}
And this does the receive:
int yudpsocket_receive(int socket_fd, char *outdata, int expted_len, char *remoteip, int* remoteport) {
struct sockaddr_in cli_addr;
socklen_t clilen = sizeof(cli_addr);
memset(&cli_addr, 0x0, sizeof(struct sockaddr_in));
int len = (int)recvfrom(socket_fd, outdata, expted_len, 0, (struct sockaddr *)&cli_addr, &clilen);
char *clientip = inet_ntoa(cli_addr.sin_addr);
memcpy(remoteip, clientip, strlen(clientip));
*remoteport = cli_addr.sin_port; // Maybe not right - s.b. ntohs()?
return len;
}