I have the same problem too, I don't think for now we can rely on the schedules from the car or the app. Been rarely reliable, there were even days after I woke up in the morning to find that it did not start charging as per the early morning schedule set, hence no charge but we have then to use fuel if can't wait for it to then charge.
Currently I have the car set to charge when plugged in as I don't use the schedule from the car/app, I charge via another EV charger (not Ford Wallbox or 3pin charger) but I have the schedule set on the EV charger app, so that works fine as per the schedule of the EV charger (cheap night tariffs). However as soon as i plug the car, a few minutes later I get notification from the Ford app stating that charge did not begin as per schedule. But there is no schedule set in the Ford app or car.
I reported this to FordPass support and as expected they came back to me stating that the FordPass app is not compatible with 3rd party charger, only compatible with Ford Connected Wallbox, that's the reason it throws this notification, to what extent to believe this is true, I don't think so.
So it looks from the point of view of the app, that charge when plugged in is also a schedule, if you plug it in and depending on the power states of the charger (such as a wallbox charger) it sees a plug is connected but cannot get power from it to charge (as the charger has its own schedule), then it treats this as charge did not begin as scheduled (that is when plugged).