Leviathan + Dagger vs Leviathan + Dagger

Nothing is broken here. RNG is just RNG, sometimes it's very good to you, other times it flips every time and then there's the times it just beats you bloody.

You should start to write down every single battle and note what happened, you should notice after a decent amount of data points that it is in fact just random.
I've been noting down every battle since November 20th and have so far 32 logged mirrors.
I've gone first in 18 of those 32 attempts (56% win rate on coin flip) but what's also worth noting for this thread is that I had a spell a few days back where I went first 10 times in a row. Currently I'm on a streak of 4 lost flips, but it seems pretty even for me with my still limited data sample.

Also worth noting, out of those 32 mirrors, I've lost 1 due to timeout, the remaining 31 were wins. For the one loss I did have, I was playing while doing something else that got me distracted, so most likely if I had focused on the game I would have won as it was pretty close near the end, but anyway, my win rate is 97% so far.
I use the TIE reaper as 1st reinf mirror strategy, with fury, bomber, dagger starting and I do not have crazy relic levels on my pilots, so it should really be mostly a case of learning the mirror approach, play fast and then the main loss is the time you have to spend on these battles relative to how easy it used to be.