Liquidity problems aren't uncommon even for such super-safe assets as US treasuries. US is keen to address those ASAP and usually pumps in a lot of $$ to unbloc

Liquidity problems aren't uncommon even for such super-safe assets as US treasuries. US is keen to address those ASAP and usually pumps in a lot of $$ to unblock the market if they see any issues with liquidity. Without such interventions a run on treasuries would be a possibility. This would lead to cascading failures as they are used in leveraged bets far and wide, from hedge funds to pension funds.