Co-op problem can’t connect with only one of my friends

Hi for some reason I can’t connect with one of my friends if I’m the host I can’t connect with him and viceversa, we tried on other games even in all the other bl games we can connect just fine, we tried inviting each other after every patch but nothing.
Does someone have more insight about this problem if yes have you found a way to fix it*?
Is this a bug on bl3 side?

*Except be invited from a third friend.