The Spanish case shows how tricky it is to sell your gold. Suddenly other countries found out that Spain had money from liquidating its gold and milked it dry.
Given Spain’s history it is incredible that the gold collected over centuries was spent in a few years.
The wiki article is very carefully tip toeing that there is no evidence that the Soviets defrauded or abused the Spanish, but it is hard to believe that 72% of the world’s gold reserves were visibly spent in a few years.
I did not investigate further but I understood the documents are not completely public, and my conspiracy hat tells me that is because it is a national humiliation.
At the time the Soviet Union had the Spanish government over a barrel because they were the only people who could/would supply significant quantities of desperately needed weapons (the opposing Nationalists were better equipped for reasons I'm not entirely sure of).
This also contributed significantly to the Communist (Stalinist) faction winning the internecine struggle on the left against the Anarchists and Trotskyists, but the quid pro quo was loyalty to the Soviet Union.
In hindsight we know they lost anyway, so this seems really silly, but at the time everyone involved believed they were in a completely existential struggle against fascism that was more important than literally anything else.
For anyone interested Orwell's Homage to Catalonia is an excellent book although it's just one man's perspective and may not be entirely historically accurate