I’m in a similar boat. I can have two different VO2max workouts that are the exact same level, but one I can’t finish because of longer intervals. It seems that as soon as I go into that zone I’m just not able to sustain it for the same amount of time as others.
Maybe I just don’t like putting myself through agony any more. I definitely don’t treat the taste of blood after a workout as any sort of victory now!