Stablecoins, to put it simply, rely on everyone believing they can be exchanged back for 1. Once reserves become opaque, the first issue that arises isn't technical problems on the blockchain, but a loss of confidence leading to a bank run: if you think others will run, you'll want to run first. Recently, during the airdrop season, task platforms have become more anti-witchcraft and the points system is as competitive as going to work, making people more likely to treat "redeemable" as a default assumption. Any small disturbance can cause everyone to hit the sell button collectively.