It's what I call "screening" failure. The wrong person was brought into the interview for the wrong position. When somebody fails fizzbuzz, this is 100% the fault of the hiring company/recruiter. Fizzbuzz is not a test, it's a "Lets get comfortable before the interview starts in earnest" type question. If you are a proficient developer, and you aren't able to nail that in your sleep, then somebody made a huge mistake bringing you in for an interview.

Our company has recently started doing (developer) screening by doing online real time coding, where the candidate get the opportunity to solve some real-time problems in their vertical, with whatever tools/compilers they are comfortable with (Java/Python/C/C++ and MAC Layer, PHY Layer, SQL, UI Frameworks, etc..) before they are brought in for an interview.

Nobody fails fizzbuzz in our interviews, and it means nobody is wasting interviewing time doing screening anymore.