Candidates try to squirrel out what they are being asked to do, or even who they are being asked to be, and funnel their energies towards that. When the situation is ambiguous, a so-called “weak” situation, those better at squirrelling – those with high “ability to identify criteria” (ATIC) - will put on the right performance, and those that are worse will put on Peer Gynt for the panto crowd.
Some people are better at guessing what an assessment is measuring than others, so in itself ATIC is a real phenomenon. And the research shows that higher ATIC scores are associated with higher overall assessment performance, and better scores specifically on the dimensions they correctly guess. ATIC clearly has a 'figuring-out' element, so we might suspect its effects are an artefact of it being strongly associated with cognitive ability, itself associated with better performance in many types of assessment. But if anything the evidence works the other way. ATIC has an effect over and above cognitive ability, and it seems possible that cognitive ability buffs assessment scores mainly due to its contribution to the ATIC effect.
Lesson from this (and note to self, after just applying for a job for the first time in 20 years): don't rely on the job spec and person spec. Do more research. Phone people and squirrel out what they really want. Maybe you don't even have to ask direct questions (it's not a cognitive, analytical skill), just get a feel for the vibe.