I finished the KotN quest and was using the Priory of the Nine to store my loot, but it's disappeared and the old crazy guy is back in Anvil, ranting away outside the chapel. There is nothing on the map. Not only that, I closed the game one day with $10,000 gold and when I started the next day, there was only $1500. I've been robbed!
I don't suppose there's anything I can do to get it back, is there? I don't want to reload an earlier save because I've done so many important quests since then and don't want to go through them all again.

That's odd. Maybe the Thieve's Guild is after you

Anyway, did you alter anything with the KotN file(s) or are you on console?

Yes there is some solutions, by the way if you are on PC.

It sounds almost as if you did load an earlier save.