I don't really think you can talk about him only having one bad game as a Juve coach like the one mentioned against Ajax.
The thing is, when you have to keep doing comebacks then it's because you're doing something wrong. And that was also the reason I said I liked the Allegri football from 2014-17.
His last two years you had too many bad moments in the KO rounds as I remember it, the ones against Tottenham where you let go of a 2-0 lead, the home leg against Real Madrid, the away leg against Atletico and then the Ajax game.
It's always great when you can achieve comebacks, no doubt. But if you have to do comebacks very often, then it means you messed something totally up in the first game and even with the comebacks is it dangerous to put yourself in this situation again and again because you fuck up your tactics and approach in the first leg, at some point you won't be able to bounce back and it bites you in the ass.
Allegri from 2014-17 actually played what I would consider close to flawless CL campaigns, but after your final in 2017 it only went downhill as I see it.