What should a team do when a creative review ends with a vague no?
When a review ends in a vague no, hold off on producing more options. Ask the reviewer to say what didn't work: the underlying idea, the execution or a claim nobody could support. A general reaction is a place to start, and it doesn't count as a revision instruction yet.
In the creative judgment panel, the Dropbox representative described developing many variations and still hearing that the work had missed. She also talked about making space away from constant notifications. Both points bear on what the team does next.
Go back to the brief and the decision the work was meant to support. Sometimes the feedback changes the assignment. Sometimes it shows the team read the assignment differently. Either way, confirm the revised direction with whoever can make that decision.
Then match the next step to the problem. An execution issue may need a focused revision. A weak concept may call for more customer understanding or a new creative approach. More headlines won't answer every kind of objection.
I'd give the team a bounded period to think without asking for a stream of new assets as proof of progress. They could examine the customer question, compare relevant work or talk the idea through together. Agree on what comes back, like two really different directions and the reasoning behind them.
Check those directions against the clarified brief before anyone asks for full production. That keeps the next round tied to the real objection, and the team doesn't have to keep producing until something gets accepted.