That happened in May-Jun 2019. Auditor's report came out that Tether was insolvent, there was a run on the bank, Bitfinex suspended redemptions of Tether, Bina

That happened in May-Jun 2019. Auditor's report came out that Tether was insolvent, there was a run on the bank, Bitfinex suspended redemptions of Tether, Binance suspended trading in Tether. The price of Bitcoin went up, from about $5200 to $11,000. Why? Because with Tether out of the picture, Bitcoin is the next most stable cryptocurrency (at the time, there was not enough DAI or USDC in circulation to absorb all the Tether money, though those "stablecoins" traded at a premium of about $1.06/$0.92 against Tether). If you're in the cryptocurrency ecosystem, it's usually because you don't want to keep any of your wealth in $USD, so when Tether was declared insolvent all of the money there rushed into BTC.