Only some of a participant's team members are appearing when they check in their participant center. When I check on the backend, they are all there. Why is only a subset of the members showing online?
Participants can delete address book entries including team members. If they deleted a team member last year, that information will be retained for this year as well. So this can happen if the participant deleted someone from the address book who should be a team member this year. Support can reset the team membership for a given participant. Note that the whole team will come back which could create duplicates for the participant if the participant recreated any of the team members.