Only the first clear for each guardian counts... master or not.
That said, i've had the same same amount of bad luck as you..... it's their stupid RNG, designed to frustrate the crap out of us.
And as far as those boosters are concerned, I'm begining to think that they are just a ploy.
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Yup, ploy all of the way. No way I waste the huge time it would take to fetch essences solo and get like a 1% buff. The memories wete cool and I think beating it on Master should be a goal in dungeons. But Soloing it, or Soloing Flawless, or Playing it with all clan are not good triumphs. Certain people dont make friends and some people get bored playing alone.