One possibility that can cause this to happen is if you do not have enough 500 mile upgrades in your account. In that case, your name will not appear on the airport standby list.
When you check in using the app, it will tell you that you have been added to the airport upgrade list. If you do not get this message, that would be the appropriate time to call in. By the time you get to the gate, a lot of agents aren't willing to take the time to troubleshoot because they have a lot of other stuff to do (and especially if there are already 20 names on the upgrade list).
As far as pilots in F, they could be anything from non-rev to EXP to positive space company travel.