Markarth Heist Job Item (Thieves Guild Side Quest) missing from Lockbox

[AniGa]

Hey. Hope someone can help me here.
I have a Thieves Guild Heist Job in which I am supposed to steal a Flawless Garnet from the lockbox in the Markarth Stables.
I got in no problem, just waited for the dog to look the other way... but the Flawless Garnet is not in the lockbox; I only found some gold and an ingot.

I already tried reloading a previous savestate and trying it again, but to no avail; the Flawless Garnet is not there.

Did someone else encounter this problem? If so, did you manage to fix it?

I'd hate to go home without success and just quit the job due to a bug... I nonstop-roleplay in Skyrim, so that would be bluergh.
I don't even care if I have to place the Flawless Garnet there with a console command and then steal it - I just want the quest to work.

Hope someone has advice for this situation.


Greets,
AniGa