I've run through the game 6 times now. First four, trying all difficulties and various choices, had no issues (Xbox One version).
The fifth and sixth run-throughs (normal difficulty) I have encountered the exact same issue when I enter the pit. If I either try to manually save the game, or run long enough so auto-save attempts, the game crashes out. The situation seems pretty unique to hit and could be related to Nyoka somehow. Here's what I do:
Kill everyone in Edgewater, let the deserters have it, then kill them.
Do all Sub-light quests.
Do all Groundbreaker quests.
Kill everyone in Stellar bay.
Do all Iconoclast quests, kill Graham, let Zora rule.
Complete all follower quests.
Send Felix with the pirate guy.
Send Minister's message, take only 27% of the chemicals for Welles.
Kill everyone in Byzanthium.
Kill Ellie's parents, she's pissed and leaves.
Kill everyone except Sublight on Groundbreaker.
Parvati leaves because I killed Junlei
Go back to Monarch and kill Hiram. Nyoka is pissed but doesn't leave.
If she's in the party she keeps saying "Can we talk" but when I talk with her, she has nothing new to say.
The game saves fine on Tartarus just prior to entering the pit. But once I'm in there, it will always crash out. I wanted to see how the game would handle killing almost everyone I met along the way. Having it lock up when I'm only about 20-30 minutes from the end is a bit frustrating.