Clean House - Beneath the Mountain achievement

[Wainwright]

So, the description for the achievement says to like, secure all of the loot from the vaults and mountain-top in the escape helicopter. The vault has only 4 lootable items, and I think the mountain-top has 6 lootable items, but the question I really want to ask is:

What's the total amount of lootable items?

[ryan]

Well 10. It is.
If you don't believe me open all the green crates you can find on the mountain top.

[Wainwright]

Well, I do believe you because I got a result of 10 bags on the stats/exp screen, but I still didn't get the achievement.
I heard from other responses on other discussions that the achievement should appear once all 10 are bagged, but I didn't get that notification nor did it show up in my achievements.
I don't think difficulty is a requirement, but I did it on Mayhem, regardless.
Nonetheless, thanks for your response, though.

[Strider]

I sometimes get up to 12 bags total. I'm not totally sure on this since I've got the achievement quite early in the heist's release but it seems to fluctuate between 10-12 bags total when I search the helipad.

[Salem]

No. There are always 10 bags max, 6 in green crates and 4 in the vaults.