An athlete I coach is not in my Athletes list. Why?

The Athletes list is built from subscriptions: a person appears once there is a coaching arrangement behind them. Someone who shared their data with you before the coaching area existed has a sharing link but no arrangement, so there is nothing for the list to show and their record page will not open. What fixes it is the normal route: a prospect, an agreement, and the athlete accepting it. If you have athletes in that position, use Ask for help and the Trailwise team will sort out the record behind them.