Non existent mission item in another castle

I did the mission but it said there was a mission item I apparently missed so I checked out videos to see if I might see where to find it but when the people in videos played I also saw them completing this mission and not having that item.

It’s been a long time since I did that mission so I don’t remember where this is exactly, but here’s that fifth item:

Sorry for the low quality.

It’s in the gas room in the bunker. Right as u walk in there is a gas canister on the ground pick it up to get the ladel.