There is a standard setup in AR system options to make salesperson mandatory, you can use that option (there is a check box if you select that one system
will make this as mandatory by its own.)
Regarding these patches, you have to check what exactly these patches is doing with the system. (you can take help from DBA persons).
The personalization was not implemented from scratch. It is just a clone of production environment where it is working fine.
Even in DEV, it is working fine some operating units.
For the new operating units that we are rolling out , it is not taking effect.
I will followup on your update and test it out