20 minutes slower is quite a big deal for the bike-leg meaning your power was down significantly. With power down that much you could have been over trained and fatigued coming into it. Were you strong in your taper workouts?
TR intensity can be pretty hard to maintain for athletes of our age. I am a similar age and needed to switch to a 3 week training block and 1 week rest period. I feel the standard plan was too much for me and my circumstances. Your coach would have managed this for you previously but now you need to take the actions into your own hands.