I've had this problem too. Some years they eat it, and other years they dont.
Mast production is a factor, but it isn't all there is to it. I have had two years in a row of heavy mast, but they still feed in my plots too. Looks to be typical, feeding more on acorns, but hitting plots as they go through.
I think the weather has a major impact on food plots and deer. I believe it was three years ago, it was so warm in November, that my oats and wheat was about a foot tall and started to produce seed heads.
Once a plant somewhat matures, I do not think they eat it. They like it tender.
To keep that from happening, I try to wait until late September to plant.