Why is my custom field on ProductionOrderPrintProcessFilter DAC extension not returning a value?

Screen modifying: Print Production Orders (AM511000) - in version 22R2

Overall Goal: Pass Report ID from custom selector to be used in the print report process instead of reportID off line item.

Issue: custom field returns null instead of selected value

I have created a custom selector that lists Report IDs from the AM module on the Print Production Orders form, and I have modified the BuildReportRequiredException method so that I can pass the selected Report ID through to be printed for any processed records. However my custom field in the ProductionOrderPrintProcessFilterExt DAC extension is returning a null value every time instead of the selected value.

Note: I’ve even tried creating a simple text field within the DAC extension and that also returns null when trying to process the record instead of the value entered. 

Graph Extension: 

namespace PX.Objects.AM
{
  [PXProtectedAccess]
  public class ProductionOrderPrintProcess_Extension : 
  PXGraphExtension<PX.Objects.AM.ProductionOrderPrintProcess>
  {
    [PXLocalizable]
    public class ReqMessage : PX.Data.BQL.BqlString.Constant<ReqMessage>
    {
      public const string reqMess = "Print Production Report ID required.";
      public ReqMessage() : base("Print Production Report ID required.") { }
    }

   #region Event Handlers


   [PXOverride]
   public virtual PXReportRequiredException 
   BuildReportRequiredException(PrintProductionOrders prodItem,
   Dictionary<string, string> parameters, string reportID, PXReportRequiredException ex)
   {
      ProductionOrderPrintProcessFilter row = Base.Filter.Current;
      ProductionOrderPrintProcessFilterExt pExt = 
      row.GetExtension<ProductionOrderPrintProcessFilterExt>();
      if (pExt == null) throw new PXException(ReqMessage.reqMess);
      var repID = pExt.UsrPrintProdReportID;
      if (string.IsNullOrEmpty(repID)) throw new PXException(ReqMessage.reqMess);
      reportID = repID;

      return PXReportRequiredException.CombineReport(ex, reportID, parameters);
   }

    #endregion
  }
}

I’m able to see that my extension is returned properly as pExt is not returned null, however the field being accessed (UsrPrintProdReportID) is returning null.

DAC Extension:

namespace PX.Objects.AM
{
  [PXProjection(typeof(Select<NotificationSetup,
  Where<NotificationSetup.module, Equal<PXModule.rq>>>), Persistent = true)]


  public class ProductionOrderPrintProcessFilterExt : 
PXCacheExtension<PX.Objects.AM.ProductionOrderPrintProcess.ProductionOrderPrintProcessFilter>
  {
        public class ConString : PX.Data.BQL.BqlString.Constant<ConString>
        {
        public ConString() : base("AM6250") { }
        }



        #region UsrPrintProdReportID
        [PXString(15, InputMask = "CC.CC.CC.CC")]
        [PXUIField(DisplayName = "Print Production Report ID")]
        [PXSelector(typeof(Search<PX.SM.SiteMap.screenID,
        Where<PX.SM.SiteMap.screenID, Like<Common.AMwildcard_>, 
        And<PX.SM.SiteMap.url, Like<PX.Objects.Common.urlReports>>>,
        OrderBy<Asc<PX.SM.SiteMap.screenID>>>), typeof(PX.SM.SiteMap.screenID), 
        typeof(PX.SM.SiteMap.title),
        Headers = new string[] { PX.Objects.CA.Messages.ReportID, 
        PX.Objects.CA.Messages.ReportName },
        DescriptionField = typeof(PX.SM.SiteMap.title))]

        public virtual string UsrPrintProdReportID
        {
            get { return this._UsrPrintProdReportID; }
            set { this._UsrPrintProdReportID = value; }
        }
        public abstract class usrPrintProdReportID : 
        PX.Data.BQL.BqlString.Field<usrPrintProdReportID> { }
        protected string _UsrPrintProdReportID;
        #endregion

        #region UsrTestReportID
        [PXString(15)]
        [PXUIField(DisplayName = "TestReportID")]

        public virtual string UsrTestReportID { get; set; }
        public abstract class usrTestReportID : 
        PX.Data.BQL.BqlString.Field<usrTestReportID> { }
        #endregion
  }
}

Is there something I’m missing when extending the ProductionOrderPrintProcessFilter?

Thank you.