It is unclear if any specific catalyst prompted this collapse but the move in Ethereum followed reports, as CoinTelegraph points out, that the Ethereum smart contract of 0x decentralized exchange (DEX) protocol has been suspended after a vulnerability has been uncovered in its code, the project's team announced in a Medium post published on July 13.
Per the announcement, third-party security researcher samczsun warned the 0x team about the vulnerability in the exchange smart contract and, after evaluating it, the team suspended the exchange's contract and the AssetProxy contracts.
The vulnerability would have allowed an attacker to fill certain orders with invalid signatures. The announcement reassures that one has exploited this vulnerability and no users have lost their funds.
But, we note that the only consequence is apparently a temporary suspension of the service.