This sounds a bit like a whistleblowing question, but that's OK, occasionally. I think the CEO should know who is blocking the process. If sustainability is important to you as CEO, and reporting is a key part of that, you need to have set your expectations clear. If your people are blocking progress, you might want to consider how this should affect their performance review, bonus or career development prospects. As a minimum, you might want to talk to them to find out what prevented them from being collaborative.