We're currently tracking an issue where jerseys aren't being remembered as being selected after Zwift is closed. This only appears to affect jerseys unlocked through promo codes, and only if the promo code was entered through the web dashboard at my.zwift.com.
While we don't have a workaround for this issue, it should be resolved in an upcoming update. You can watch this post for updates.
Thanks for your patience and understanding as we work to fix this!