Custom selector field working in one tenant, but errors in second tenant

Publishing was performed using the Publish to Multiple Tenants button.

POOrder.CustomField is a selector showing a filtered list of Non-Stock Items belonging to a specific CUSTOMCLASS Item Class.

In Tenant 1, where the customisation was published from (to all tenants):
The selector correctly displays the list of items in the CUSTOMCLASS Item Class, allows selection in the custom field, and saves the Purchase Order without error.

In Tenant 2, the same custom field correctly displays the list of items (different items in this tenant, but still belonging to the matching named CUSTOMCLASS Item Class), allows selection in the custom field, but on save give this error: 'CustomField' cannot be found in the system.

Here is the DAC Extension:

  public class POOrderExt : PXCacheExtension<PX.Objects.PO.POOrder>
  {
    #region CustomField
    [PXDBString(50)]
    [PXUIField(DisplayName="Custom Field")]
    [PXSelector(
      typeof(Search<PX.Objects.IN.InventoryItem.inventoryCD
          , Where<PX.Objects.IN.InventoryItem.itemClassID, Equal<customfieldItemClassIdConstant>>>),
      typeof(PX.Objects.IN.InventoryItem.inventoryCD),
      typeof(PX.Objects.IN.InventoryItem.descr),
      DescriptionField=typeof(PX.Objects.IN.InventoryItem.descr))]
    public string CustomField { get; set; }
    public abstract class customField : IBqlField { }
    public class customfieldItemClassIdConstant : PX.Data.BQL.BqlInt.Constant<customfieldItemClassIdConstant>
    {
        public customfieldItemClassIdConstant()
            : base(FindCustomFieldItemClassID("CUSTOMCLASS")) { }
        
        public static int FindCustomFieldItemClassID(string itemClassCD)
        {
            PXResult<INItemClass> result = PXSelect<INItemClass,
                Where<INItemClass.itemClassCD, Equal<Required<INItemClass.itemClassCD>>>>
                .SelectWindowed(new PXGraph(), 0, 1, itemClassCD);
    
             if(result == null) return 0;

            INItemClass customfieldItemClass = result.GetItem<INItemClass>();
            if(customfieldItemClass == null)
            {
              return 0;
            }
            else
            {
              return customfieldItemClass?.ItemClassID ?? 0;
            }
        }
    }
    #endregion

I cant work out why it would work in one tenant, and not the others as the fields and selector is behaving as it should in all tenants, but the save of the selection is erroring, even though the database column is shared by all tenants.