According to Jackfrags' video all you need to proceed to get the gun on Passchendaele was to equip one of the front phantom dogtag, one back phantom dogtag and the Escalation M1917 LMG skin.
For the front dogtag I only have "The Omen" dogtag since it was the easiest to do.
So i equip all three and jump into Passchendaele to finally get my gun.
However inside the tunnel like 9 levels in, just before the next button, I heard an eerie sound (just like those after you completed other tasks) and suddenly my health dropped to zero and died. Happened to me twice, i even recorded it.
Do i really need to get the rest of the phantom dogtag before i get this stupid gun? because it is ridiculously hard to get the other two. especially on console.