Since you mentioned you train outside, I’m willing to bet you are running into an ongoing bug with the prediction, where outside workouts trigger predictions to tank very quickly.
It’s said to be on the very top of the ToDo list of the devs, but still unresolved for now AFAIK.
For now, best ignore it and check again once the issue is resolved. Also, it only affects predictions, workout selection and actual FTP calculation are working perfectly fine