Can't detail steel reinforcement in custom parametric pier - "element not valid for tool"

I've added a custom, parametric pier to an OBM model of a bridge I'm working on, and I'm now trying to add reinforcing steel to it; however, when I boot up the ProConcrete workflow and try to add reinforcing steel to any of the columns/caps/drilled shafts, it gives me a tooltip telling me "Element not valid for tool."  I've also attempted to add the reinforcement directly into the cell file and then add the custom pier to the main model; however, all of that reinforcement goes away when I've tried that.

SideStepBent (Bent 2).cel