Well OpenAI say users' names, emails and locations have been divulged, one of them is going to accept there was a "breach"
If Mixpanel is subprocessor of GDPR'd data from OpenAI, OpenAI is obliged to notify affected European customers about the data breach within 72hrs.
OpenAI was sending that data to MixPanel. If anything, OpenAI is culprit for sensitive data leak. There’s absolutely no reason to send that data.