Not really sure how all these stable coins work but how did a stable coin that is supposed to be equal to one US Dollar go down in price? 
USDC de-pegged with USD because of the event of Silicon Valley Bank issue. It was said that "the depegging happened after Circle, the issuer of USDC, disclosed on Friday night that some $3.3 billion worth of the cash reserves that back USDC remain held at Silicon Valley Bank, which was shut down by California financial regulators this week after a bank run."[1]
It became worse when some crypto exchanges temporarily suspended USDC conversions[1], but as of this reply, USDC somehow recovered, and it was assume that USDC will be back to its normal operation by this Monday.
[1] https://decrypt.co/123211/usdc-stablecoin-depegs-90-cents-circle-exposure-silicon-valley-bank