Hope the below steps would help you find the reason why subject is not having value
Put a breakpoint on a that assign activity
For that right click and add a breakpoint
Next Run in debug mode so that bot will excite till that breakpoint and once it has reached you can check the value of those two variables in Local panels
If value is found for those variables in local panel then fine
If not then we need validate with the two assign activities where we get the value for those two variables
I could see u have used for each row activity and getting value from a specific columns
Check whether the column is mentioned rightly and u have value in those columns as well