How often does it occur?

I am playing a coop campaign with a friend and for lolRP reasons, I was waiting for a British mission but always got French or American ones, which I declined (like 3 or 4 times) until in the end my friend got a British one, went with that and I haven't seen an offer since.

Is it bugged, so it only lets one of the players in coop choose one or does it not happen after a certain time?

Thanks in advance.