I was playing Roguebook yesterday, it's a deckbuilder like Slay the Spire, but you choose levels by exploring a hex map.
After repeated tries over a total of 13-14 hours, I beat the game for the first time. That run was an hour or so. The RNG had given me this build that made enemies bleed, that allowed me to make them bleed more, then double that bleed.
I also had daggers that I could get into my hand and use for zero mana, then double those daggers and double then again.
I had a modified card that with the highest block I've seen, that soaked up almost all damage - when it was lucky enough to appear.
I beat the final boss - a close match! - and got an achievement saying only 20% of players had beaten the final boss.
Then the game crashed. I could hear it playing in the background, but I had a screen full of red text and code errors.
I kept the achievement and lost everything else. I should have earned XP, modifiers, treasures, more cards and god knows what else. I suspect the game runs online, even though it's PvE. (The devs other game Faeria is like this.) If there's a crash, I suppose the server isn't notified about my game status.
Who's to say I'll ever have that combination of cards and circumstances again?
What's your most annoying crash?