RowSelected warning misses the first row.

I’m pulling my hair out a bit. I was helped along on this project by another user and I think I'm missing something here: 

I need each row to show a warning containing the various vendor prices. When I use the RowSelected event the top row value gets cleared out and when I change vendors it no longer updates the price. See images for expected behavior and current result.

(originally I was using RowUpdated (which worked) but then I would have to update the row before the warning would occur)

Any help would be greatly appreciated

using PX.Data;
using PX.Data.BQL;
using PX.Data.BQL.Fluent;
using PX.Objects.AP;
using PX.Objects.PO;
using System;
using System.Text;

namespace PX.Objects.SO
{
    public class POCreate_ExtensionAI : PXGraphExtension<POCreate>
    {
        public static bool IsActive() => true;

        #region Event Handlers

        protected void _(Events.RowSelected<POFixedDemand> e)
        {
            var row = (POFixedDemand)e.Row;
            if (row == null || row.InventoryID == null || row.OrderQty == null) return;
            PXUIFieldAttribute.SetWarning<POFixedDemand.effPrice>(Base.FixedDemand.Cache, row, null);
            string msg = GetQtyMessage(row.InventoryID, row.VendorID, row.OrderQty, null);
            PXUIFieldAttribute.SetWarning<POFixedDemand.effPrice>(Base.FixedDemand.Cache, row, msg);
        }

        protected decimal GetItemQtyTotalOnPO(int? inventoryID)
        {
            decimal retVal = 0;

            foreach (POFixedDemand line in Base.FixedDemand.Select())
            {
                if (line.InventoryID == inventoryID)
                {
                    retVal += line.OrderQty ?? 0;
                }
            }
            return retVal;
        }

        protected string GetQtyMessage(int? inventoryID, int? vendorID, decimal? lineQty, DateTime? requestedDate)
        {
            if (inventoryID == null || vendorID == null || lineQty == null) return null;

            StringBuilder p = new StringBuilder();
            decimal orderQty = GetItemQtyTotalOnPO(inventoryID);
            if (requestedDate == null) requestedDate = Base.Accessinfo.BusinessDate;




            var prices =
                SelectFrom<APVendorPrice>
                     .Where<APVendorPrice.inventoryID.IsEqual<@P.AsInt>
                        //.And<APVendorPrice.vendorID.IsEqual<@P.AsInt>>
                        .And<APVendorPrice.effectiveDate.IsLessEqual<@P.AsDateTime>
                        .Or<APVendorPrice.effectiveDate.IsNull>>
                    .And<APVendorPrice.expirationDate.IsGreaterEqual<@P.AsDateTime>
                        .Or<APVendorPrice.expirationDate.IsNull>>>
                .View.ReadOnly.Select(Base, inventoryID, requestedDate, requestedDate);

            var vendors =
               SelectFrom<Vendor>
               .LeftJoin<APVendorPrice>.On<Vendor.bAccountID.IsEqual<APVendorPrice.vendorID>>
               .Where<APVendorPrice.inventoryID.IsEqual<@P.AsInt>>
               .View.ReadOnly.Select(Base, inventoryID);

            if (prices == null) return null;

            p.AppendLine("Pricing available:");
            foreach (APVendorPrice price in prices)
            {

                string vendorName = "empty";
                foreach (Vendor vendor in vendors)
                {
                    if (vendor.BAccountID == price.VendorID)
                        vendorName = vendor.AcctName.ToString();
                }

                p.AppendLine(vendorName + ":");
                p.AppendLine($"${price.SalesPrice:n2}");

            }
            p.AppendLine("");
            p.AppendLine($"You have {orderQty:n2} on this Purchase Order");
            return p.ToString();
        }
        #endregion
    }
}

expected behavior: