Custom class with parent child sync failing

Hi,

We have a custom module with two classes. A parent class and a child class (1-n).

Syncronisation of the parent type works as expected.

When we try and syncronise content of the child type from a staging server to production, the sync fails with this error:

SyncServer.ServerError: Exception occurred: [DataConnection.HandleError]: Query: 

INSERT INTO client_ModuleItem ([ModuleItemGuid], [ModuleItemLastModified], [ISBN], [ListOrder], [ModuleID]) VALUES (@ModuleItemGuid, @ModuleItemLastModified, @ISBN, @ListOrder, @ModuleID); 

SELECT SCOPE_IDENTITY() AS [ID] Caused exception: Cannot insert the value NULL into column 'ModuleID', table 'kentico.dbo.client_ModuleItem'; column does not allow nulls. INSERT fails. The statement has been terminated.

A profile on the destination server shows that ModuleID is null rather than the translated id of the parent object on the destination server.

We have followed this doc: https://docs.kentico.com/k11/custom-development/creating-custom-modules/setting-the-type-information-for-module-classes/enabling-export-and-staging-for-the-data-of-classes

The TYPEINFO of the child class has the parent ID field and type set in the constructor.

SynchronizationSettings set with LogSynchronization = SynchronizationTypeEnum.TouchParent

Saving a child item on the source server creates a syncronisation task of the parent type with all the child items in the task.

This tells me the parent-child relationship between the classes along with TouchParent is working as expected.

We have also created a Custom ID Translation Module as described here: https://docs.kentico.com/k11/custom-development/handling-global-events/deploying-objects-with-custom-id-fields

ColumnsTranslationEvents.TranslateColumns.Execute += TranslateColumns_Execute;

private void TranslateColumns_Execute(object sender, ColumnsTranslationEventArgs e)
{
    if (e.ObjectType == ModuleItemInfo.OBJECT_TYPE)
    {
        e.TranslationHelper.TranslateColumn(e.Data, "ModuleID", ModuleInfo.OBJECT_TYPE);
    }
}

Where ModuleInfo is the parent type and ModuleItemInfo is the child type.

This is on Kentico 11.

Any idea what we are missing here?

Thanks, Stephen