(I'm not sure if my first attempt to post this bug went through. Mods please delete if this is a duplicate.)
The same bug (reported above by Nealypants) just happened to me. For more details on the specific circumstances if it's helpful reproducing:
I had just completed HRS-1084 as part of the "Ice Palace" side quest. My companions during the mission were Nyako and Ellie. I re-entered the ship with the intention of returning to Groundbreaker to report back to Lilya.
Upon re-entering the ship, ADA informed that Ellie and Max were having an argument in the kitchen. Before proceeding, I stopped to check on Parvati. She was leaning against the shelves in the cargo bay. She had no new dialogue, so I exited her dialogue and proceeded upstairs.
I stopped and listened to Max and Ellie's dialogue (where Ellie was attempting to annoy the now-enlightened MAX) to its completion where Ellie walked away toward her bunk.
I stopped and spoke to Max and checked his "tell me again your opinion about the sophists" line since I hadn't yet listened to that one.
I exited dialogue with Max and then attempted to speak with Nyako who was in her normal position of leaning on the counter.
As soon as I selected to speak to Nyako, the "Don't Bite The Sun" quest line marked itself as failed/botched. When I checked the quest log, it said that it was because Parvati had been killed.
I went to check for her around the ship and could not find her anywhere. She had vanished somewhere.
Her death did not make any sense because we were all completely safe on the ship and I had just talked to her. I also am not playing on Supernova, so my understanding is that companion death should not even be possible.
My ship was parked at HRS-1084 during this entire series of events.
I reloaded the save to the point right before I re-entered the Unreliable, which brought Parvati back to life. There were new events when entering the ship this time, and instead of talking to anyone, I just hirried straight to Groundbreaker in case it was some kind of issue with HR-1084. It did not happen again, thankfully!
It appears something seems to happen where it is possible for Parvati to fall through the ship? enter a kill zone? or otherwise commit suicide? I didn't witness the actual event.
