Maybe this has changed, but I was always under the assumption that the chest past Salazar (in the big room, not the smaller loot room) was a one-shot. If so, I was also under the assumption that an Epic was always guaranteed, but today I got a legendary instead of an Epic. I haven’t found that many legendaries, so I am unsure if this is normal.
this was changed in the last or before last patch if i remember correctly. You can now get legendaries instead of epics out of oneshot chests if you lvl is 50+ (chances increasing on elite and even more on ultimate)