Crossplay connecting issues

We are used to play with my boyfriend in crossplay (him on ps4, and me on PC). But lately as we wanted to play, I could not go in his world. It is loading and then I get a message "Connexion au monde impossible" (something like connexion to the world is impossible). We tried to do many things to make it work, but it doesn't. And I see his logo in grey like if he wasn't connected (but he is, and a friend of us gets all of his invitations on PS4). 

 

How can we fix this ? 

Thanks,