Grid column value disappears when clicking Selected checkbox in Processing screen

I have a processing screen with PXFilteredProcessingJoin where the main DAC is Customer with LeftJoin<CustomTable> and LeftJoin<Location>.

In the grid I display Location__CPriceClassID field from the joined Location DAC.

Problem: When I click the Selected checkbox on a row, the value in Location__CPriceClassID column disappears. It comes back when I click the checkbox again.

Here is my view

[PXFilterable]
public PXFilteredProcessingJoin<Customer, CustomFilter, 
    LeftJoin<Location, On<Location.locationID, Equal<Customer.defLocationID>>,
    LeftJoin<CustomTable, On<CustomTable.customerID, Equal<Customer.bAccountID>>>>,
    Where<CustomTable.example, Equal<Current<CustomFilter.example>>,
    And<Where<Customer.lastModifiedDateTime, GreaterEqual<CustomTable.LastUpdatedDate>, 
    Or<CustomTable.LastUpdatedDate, IsNull>>>>> Customers;

and delegate

public virtual IEnumerable customers()
{
    List<PXResult<Customer, Location, CustomTable>> listCustomers = new List<PXResult<Customer, Location, CustomTable>>();
    CustomFilter filter = Filter.Current;
    if (string.IsNullOrEmpty(filter.example))
        return listCustomers;

    PXResultset<Customer, Location, CustomTable> customers = null;
    if (filter.example2 == true)
        customers = PXSelectJoin<Customer,
            LeftJoin<Location, On<Location.locationID, Equal<Customer.defLocationID>>,
            LeftJoin<CustomTable, On<CustomTable.customerID, Equal<Customer.bAccountID>>>>
            >.Select<PXResultset<Customer, Location, CustomTable>>(this);
    else
        customers = PXSelectJoin<Customer,
            LeftJoin<Location, On<Location.locationID, Equal<Customer.defLocationID>>,
            LeftJoin<CustomTable, On<CustomTable.customerID, Equal<Customer.bAccountID>>>>,
            Where<CustomTable.example, Equal<Current<CustomFilter.example>>>
            >.Select<PXResultset<Customer, Location, CustomTable>>(this);

    foreach (PXResult<Customer, Location, CustomTable> custom in customers)
    {
        Customer customer = (Customer)custom;
        CustomTable customRecord = (CustomTable)custom;
        CustomerExt customerExt = customer.GetExtension<CustomerExt>();

        if (customerExt != null && customerExt.IsActive != true)
            continue;

        if ((customRecord == null || string.IsNullOrEmpty(customRecord.example)) && filter.example2 == true)
            listCustomers.Add(custom);
        else if (customer.LastModifiedDateTime >= customRecord.LastUpdatedDate)
            listCustomers.Add(custom);
    }
    return listCustomers;
}