Interesting, like this area you mean? Might have been a problem with the concrete mix or not vibrated correctly in the forms. Or the connection detail for those sound panels may have caused some stress in the concrete leading to damage. If the rebar was green then it was coated, so it's definitely not a corrosion problem.
Here's hoping the concrete was removed intentionally for a positive reason, and not as the result of (or investigation into) quality issues...