* Youth. People who have very recently studied these things in school, and use the same languages as the interviewers, have an advantage.
* Free time. People who have families (for example) might have less free time to study "Cracking the Code Interview" and such.
* Absence of anxiety. This disadvantages women, minorities, and people with psychological conditions that should be covered by ADA. Also, people whose financial situation is precarious will be more anxious than those who don't need the job, independent of which is actually a better candidate.
* Conformity. People who can recognize the flaws in a measurement technique, and who have the strength of character to push back against its application - both good qualities for a candidate - will self select out.
There's a lot of overlap among these, of course. There are better ways to measure "general IQ" and "grit" (which are both questionable concepts anyway). I've passed every such interview I've ever taken, but I refuse to administer them (despite the fact that my refusal has carried a quite tangible cost) because whatever benefit they provide is outweighed by their many flaws.