Originally Posted by fromelette

I'm beginning to wonder about the bloom drop rate in advanced. So far it has been 9-10 runs and no blooms... Last map has quite a difficulty leap compared to the others and I can't clear it yet.

Indeed, don't bother wasting time and stamina on ?-3. I've cleared ?-4 twice so far and gotten the drop both times. You do not need to clear everything on the ?-4 map, just the final boss to reach the chest. Look for a stronger helper squad.
Otherwise, you still have time to farm normal maps and strengthen your teams.