Well, I disagree with your use of the word “anonymous.” Gender, national origin, and ethnicity are frequently easy to guess (at least at the level of “is not a white, American-born male”) via voice. I know you tried voice masking and it didn’t help equalize the results wrt gender, and I don’t have a better suggestion, so I’m not blaming the process, for not attempting to remove bias. This criticism applies to both the mock interviews and the real interviews.
Bias creeps in in other ways, too. I have done both on interviewing.io as a candidate. You probably remember how Instacart has interviews on your platform under the terms that it was just an informational chat, and anyone who met the criteria to interview would then get a real technical interview. I did the informational chat and was then not interviewed after deanonymizing. And, BTW, after I emailed support I never got my technical interview, nor was I given any sort of resolution or information about what happened.
It’s a good experiment, but it falls short of what I’d call “anonymous” and doesn’t really remove very much bias in the overall process.