Can't change characters in openworld or bounty missions

[Arwen]

The only way I can change characters is at a control station or if I run into the character I want. I can't find any way to pick a character from the big list outside of those, and that makes quite a few things impossible (I will be stuck in bounty missions with two characters who don't have the skills needed), In free play I get the usual cast of (10?) characters, but outside of those I can't change into anybody else either.
I've played the game to 100% before and this was not an issue, so I have no idea what happened. Does anybody know what to do here?