I have a flight this coming Friday, and my upgrade to C+ wasn't clearing my second segment (guessing because it wasn't +72 hours before that leg). I know this is sometimes solved by deleting and then re-adding in your FF number, so I tried to do that. Interestingly, I get this message: "Whoops! We're sorry, we are unable to change frequent flyer accounts once travel has begun." Except it hasn't - its a simple one-way flight (LAS-LAX-BOS). I get the same error online and in the app. Strange!