The difference now is that professional market participants act on this "theory" by physically moving a significant amount of gold from UK to US. And "weeks-long" withdrawal queues certainly do not look great and confidence inspiring.
And yet this physical transfer of gold has had largely zero impact on the price of gold. Nobody was fretting about 'where will we source Poland's gold?'
Well, there's the notion that price no longer quite reflects what's going on under the surface. Certainly, it's in the interests of an entity experiencing a run on its reserves to do everything it can to obfuscate any indication that a run is taking place, including suspicious price shifts. Perhaps it's even more suspicious that such clear movement isn't being reflected in price volatility. If there were no trouble, a small shift reflecting physical movement wouldn't be too dangerous to allow to happen. But what if it wouldn't be a small shift?
And there is the example of Poland which has repatriated all of its gold from UK years prior and stories like this: https://x.com/SenatorRennick/status/1891051795159429514