I agree with Kevin Willis. We had six players: Drone mechanic 5, Technomancer 5, Solarian/Soldier 5, Soldier 5, Soldier 5, Envoy/Soldier 6. We have had no previous deaths at all, since it is fairly difficult to die in Starfinder as long as at least one character is ambulatory.
This one was a TPK. We didn't stand a chance. The Mechanic and the Technomancer had barely any time to act before dropping. The melee-optimized characters were unable to consistently hit. The ranged characters were exposed to the breath weapon and dropped. Most of us had purchased fire- or plasma-based longarms or heavy weapons prior to the scenario, and at least two with holy fusions.
We had no flight capability. While a jetpack is available, most of the people had previously used their money to upgrade their armor since otherwise Starfinder critters hit us with frightening regularity. The rest of the money was used to upgrade weapons and stock up with healing serums (which are useless in combat, but otherwise necessary). Starfinder economy is also built in a way that you are always saving money for the next item. I am unsure of the design specifications, but it felt like the assumption here was that the party should have had tier-equivalent armor, weapons, and mobility. We simply don't have the money to fine-tune our equipment for a single scenario.
I have not seen the stats for the dragon, but it had little trouble hitting our soldiers who were wearing the high-level armors discovered at the top of the wreck.
Some of us were stocked with mk 1 adaptive serums. Thermal capacitor upgrade is too expensive for a measly resist 5 considering most low-tier armors have only one upgrade slot; while it would be nice, there are other upgrades that are consistently more useful.
Unless there was significant mess-up in the battlefield description, I don't know how we were supposed to avoid the breath weapon. The top of the hanging bridge is flat, with a hole in the center leading down to the bottom. Both areas are coverable by a single breath weapon blast, and splitting the party between them means defeat in detail as the thing fades in to slaughter someone and then fades out again.
The dice also matter. The dragon managed to use its breath weapon almost every other round. This also created a death spiral for those dropped by the breath weapon. The lure of full attacks made people use them when the dragon wasn't faded out, and that -4 was hard on us.
The deaths happened for the usual reasons: we could not hit the creature often enough, we could not get into melee reach without one of us as a sacrificial goat, we could not take the damage (since Constitution is a tricky stat to invest in, and there was no meaningful way to mitigate the breath weapon damage), there was no place to avoid the breath weapon without sacrificing team members, the dice hated us, and there was nowhere to run.
The dragon was like a many-faceted diamond revealing new beautiful and horrible aspects on every round. It is effectively invisible between its attacks. It has evasion. It has trick attack. It had 50+ hit points remaining when it coup de graced the last of us.
Deaths happen. But TPK Fame costs are horrendous due to body recovery and negative level issues. And paying for negative levels with money is difficult at this tier.