February 2019
@EA_David wrote:
Hi all, we are looking into this. Dev confirmed here: https://www.reddit.com/r/apexlegends/comments/aqfj1g/having_an_issue_with_caustic_and_mirage_not/
In the meantime some folks have already mentioned a workaround that should help: Choose Caustic or Mirage as your default/highlighted character and leave the Legend selection time out.
Marking as Solution purely to increase visibility, we DO NOT consider this issue resolved at this time.
Thanks to everyone for the posts.
I'm going to lock the thread from replies to ensure the response by @EA_David is not missed. We want to make sure players see this while it's being looked into by the team.
February 2019
This should now be fixed.
"Fix for Xbox One is now live addressing the issue of players unable to select Caustic or Mirage after unlocking them in matchmaking. Thanks for your patience!"
Source: https://twitter.com/PlayApex/status/1096215588563632128