>Sudden tightening of credit / cash flow
Yep.
http://worldoutofwhack.com/2020/03/18/the-big-short-part-ii-villians/
"Thus, just when he was supposed to prove liquidity, he has to reduce it. His hands are tied. Even worse, he has to hedge counterparty risk with corp borrowers and that is adding to the tail spin of selling. There is no liquidity from the banks."
"We have a big fucking margin call under way."