Your invitation feature has network spillover — is the A/B valid?
InterferenceHardProblem. A change to People You May Know makes treated members send more invitations. In a member-level A/B, the treatment looks positive on connections made. A colleague says the result is trustworthy. Is it, and how would you measure the true effect?
Before you reveal: say your answer out loud, as if you were in the real interview — get your reasoning across clearly first. There is no single correct answer: reading what the interviewer is really after and defending your own thinking is what makes an answer strong.