Securities exchanges sometimes halt trading or very occasionally cancel transactions when technology glitches or “fat finger” errors cause one-off mistakes. But it’s rare for one to cancel whole sessions after the fact, or to take days to allow trading to resume freely. Yet that’s what happened with one of finance’s oldest institutions, the London Metal Exchange, or LME. Russia’s invasion of Ukraine in February 2022 sparked a period of chaos in the nickel market, exposing the vulnerabilities of