This happened to me before with another boss, and now it is the new boss. I was able to very consistently clear it with a 95%+ win rate just yesterday (September 12). But today, my win rate is maybe around 10-15% with the same preset. I have only one preset with Plume, the gear on all characters are the same, continuous battle settings are correct (prioritizing boss), and I even manually select boss to make sure they're hitting the right thing. And yet, win rate is still terrible today.
I think I have a recording of my previous clear, or one of my first clears after the release of the boss. What I am noticing is that the boss hits WAY harder now, compared to yesterday. Basically kills my characters, hence win rate goes down by a lot.
I seriously suspect this is either a bug, or a shadow buff (like how another person posted about Rengo Inferno). The RNG cannot be consistently crazy like this, and with such a drastic difference. There's something wrong.
What I noticed is that I couldn't even replay some of the previous fights in United Front from a day ago - it is the very same UF. It simply said "version mismatch". Did the balance on the server change? It feels like this is proof that something is going on.
It isn't really fun if the difficulty/stats are literally changing from the server side randomly. It should at least stay consistent between the patches. And if it cannot, ALL changes should be transparently communicated to the players. And if this is not intended, please look into this.
It is crazy how big the difference is. Very demotivating. The RNG of the drops are already very bad to begin with, and now this.