I have a python script that was initially running with ArcGIS Desktop 10.0. The script runs a bunch of analysis and then creates maps and exports to jpeg images. Prior to exporting ot jpeg, the script also defines the symbology of the map layers from some pre-defined saved layer files (.lyr). Recently, the ArcGIS license was upgraded to 10.4. The scripts works fine without any errors and produces all results. However, the symbology does not render in the new maps and ArcMAP sets some default color symbologies. Also, I checked the part (arcpy.ApplySymbologyFromLayer_management) which imports the symbologies within the ArcMAP python built-in window and it works correctly. I cannot figure out where the disconnect is in my stand alone script. Please help.
Note: Due to company policy I cannot share the code here, but any insight into the matter will be helpful.