The quietest person in the group project usually noticed the problem first. Ask them.

Quiet in a group is rarely an absence of opinion. It is often someone who processes before speaking, or who has learned that interrupting costs more than it is worth, and meanwhile they have been watching the whole thing carefully. The loudest room usually loses the most accurate read in it.

Ask the person who has not spoken what they think, by name, and then wait through the pause. Do not fill the silence for them. What comes out is frequently the thing everyone else missed.