I'm seeing breakthrough as well. One is a large irrigated lawn that is well maintained. It has a very thick turf yet the damage from grubs was accelerating at a quick pace. I hit it with duocide and all is well.
Not sure what to do for next year. I'm hoping it is just environmental factors and not a decrease in the efficacy of the product. FWIW I use a fert coated with Merit. Have used it the past two years with great success. 100% effective until now.