Is concrete produce with your mix design gives volume of 1 cum exactly.
If its design by you, cross check the specific gravities of all aggregates (Though you are using 40% FA, it might be more compare to volume, if SG is not calculated properly)
Try changing admixture, the cause most probably due to admixture you used.
Airation in most of the cases caused by admixture.
For better workability and cohesive mix increase 20mm content and reduce 10mm, this will reduce the surface area (It will also improve the strength parameter).
I can not say anything on shuttering oil, as i am not expert in it (Better you try different mould release agent and check the difference between them, it will give you idea, if oil is culprit. You can ask for sample oil from local suppliers and do test)