It sounds like he has been restarting his client, so that isn't going to fix it for him.
It might make sense just to uninstall the FAF client, re-download it, and reinstall it completely. He wouldn't have to uninstall/reinstall SC:FA itself. Just the client.
Also, I'm curious if he can join games via chat. If you look at the list of participants in Aeolus and you see someone with a yellow sword next to their name, it means they are in a lobby. You can double-click on their name and try to join the lobby that way. If he is able to join lobbies that way, it would be pretty clear that his problem is only with the custom games list.
Also, @Rotdog if you want technical help, the best place is Discord I think. For one thing, people can message you if they're ready to try to help you.
Another thing you could try: make your own custom lobby and see if people join. I would be curious if other people can see YOUR lobbies. Just put on Winter Duel and call it "all welcome." If anyone else can see it, someone will probably join within 5 minutes.