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This article goes through all of the possible explanations for the LastPass matter password incident. I encourage you to read the entire thing, not just the TL;DR near the beginning.
How did LastPass master passwords get compromised? | Almost Secure
https://palant.info/2021/12/29/how-did-lastpass-master-passwords-get-compromised/
@voltronic I hadn't even thought of the 'pass-the-hash' scenario, but sounds like a good possible culprit.