Fatigue detection can be tricky like that apparently . I went for a walk today (a red day after a longer ride yesterday) and it made Saturday a yellow day for me, suggested dropping my 60 min endurance workout and dropped my FTP detection for Sunday by a point. When I deleted the walk from the calendar, tomorrow is no longer a yellow day, no more suggestion for a rest day instead of 60 min endurance workout, and FTP prediction back up a point.