A strange fact is that Oberon's SEDs clearly say that the real Oberon died 5 years ago in the White Shark, meaning he was alive on the 13th floor before being killed by Warface. Watch the video: https://youtu.be/_Zmi4sFBLDM?t=75
The transcript of the speech of the Oberon SEDs:
"You cannot kill someone who is already dead, the true Oberon White died in White Shark five years ago, since then he is us."
The PvE Missions page still mentions that the Volcano mission has the Hardcore difficulty, but that difficulty has been removed.
If you go to the Hints and Tips page and search (CTRL+F) for Hardcore, you will see some mentions of "Hardcore co-op", I don't know if this is an error (referring to the old removed Hardcore difficulty from the Volcano mission) or referring to the current Hard difficulty of normal coops.