Error code 524

We just purchased a 1-month XBox Live access and I (parent) can play Battlefront II with multiplayer and so can my oldest son’s account. But my younger son’s account cannot play multiplayer, when he logs into Battlefront it says he is offline. When he tries to connect he gets the Error Code 524. 

I have checked their XBox online privacy settings and they both match, I can’t see why my older son can play online but my younger son cannot. They have default teen settings and both say “allow” for online access.