Have you entered all the data correctly?
If you have entered all the data correctly, then Go to Settings >> Reactions and double click on the added chemical reaction
Select the drop-down against velocity units and select kmol/[m3.s] and then click OK.
Close the settings tab and click on solve flowsheet. You will get conversion of nitrogen as 19.79% and hydrogen as 59.37%.
This minor deviation in the conversion value is due to bug fixes in the PFR code. However, the difference is not much.