Did any of your multiple professionals use an air sampler pump? They need to take multiple samples from documented locations and test the samples with potassium iodide. This will identify the area of highest chlorine concentration. Then, surfaces in that area are swab tested with potassium iodide on starch strips to detect the residual chlorine. If using the correct equipment and processes, the only way these professionals could be "stumped" is if it's not really chlorine causing the odor.