Yes. When aggregates are dry at the time of batching, the slump will drop tremendously. As I told you in the other thread, check the batching procedures.
Polyheed 997 is a mid-range water reducing admixture. Glenium 7500 is a high-range water reducing admixture. The Polyheed 997 is probable not the better one to use with a low slump mix. It is primarily formulated for slumps between 5 and 8 inches.
Again, I suspect the coarse aggregate is not saturated at the time of batching.