Adding to what Dave said...
From your description, I'm guessing you are using MAPDL, not Mechanical (in Workbench), to perform your investigation. If you want to look at results in the "smeared reinforcement" REINF265, you might try selecting those elements (e.g., ESEL,S,ENAME,,265) before making a contour plot so that you are looking at the results in those elements alone. Without the benefit of having created an investigative test case, my guess is that POST1 does not know how to reconcile a results display that includes two element types that differ as significantly as the base SOLID18x and REINF265. I suspect one plots results of one or the other, but not both together. You might start by selecting your REINF265, then plotting the fiber axial stress (PLNSOL,S,X). I would also use /ESHAPE,ON (combined with /GRAPH,POWER - the default display setting) prior to making this plot to visualize the reinforment geometry.
I hope this helps.
--Bill