I'm a senior engineer with a ton of experience, and it was an interview for a challenging role at a major; I've come to expect that sort of thing on warm-up. It's a bozo filter before the real questions, and I should have been able to do it in my sleep.

I once froze on a warm-up Fizzbuzz. Actually it was even simpler than a Fizzbuzz: print all the elements in a list.

Freezing can happen to anyone on any problem.