Unable to join friend online

I have some issues joining my friend online. When I invite him he cannot join the session and I get a message to make him the leader of the convoy. I have also tried joining him directly from the Xbox app on windows, but it did not work.

Also when he joins he gets a message that he needs to be in spring to be able to join me. I am currently in spring and him in autumn, in the singleplayer campaign. Is it not possible to join if you are in different seasons? I can also see that many of the options on the menu are not enabled until I finish the singleplayer campaign, but why should we not be able to play online free roam together before that?

In addition to this I could not find any private sessions as there were in horizon 3, is it not possible anymore?

Does anyone have a solution to this?