Is it just late to be signing up for interviews? Could that be a reason for an interview getting waived in a large urban area known to have multiple ECs/interviewers? Should a student contact admissions just to make sure there was no mistake?
Student got an email saying interview was waived. Thus my question as to whether there could have been some mistake or not, and if student should contact admissions.
No, signing up late to an interview will not result in an interview being waived (though please sign up as early as you can). Normally interviews are waived if not all candidates can be interviewed. Yes, it can happen that a city would have applicants waived (though it is rare). I know of one large city in my region where a few years back (well closer to a decade) we had 6 ECs, two years ago we had none. This year we have three. EC’s move around, they sign up and drop out. We are all volunteers, and random holes can rarely occur.
There other key question that I would need to know the answer to in order to give a clearer response. Where is the city? If it is in the US, then it is extremely rare, but possible. If it is in Europe or East Asia, less rare, but still possible (from memory, Warsaw was uncovered a few years back). If it is in China or India, then I believe it without qualm.
If you ask MIT Admissions, they may be able to set up a skype interview for you, if you do not have an assigned Educational Counselor in your area of California.