Hi Rafi,
I think you missed to enhance the structure INCL_EEW_PD_ITEM_CSF. add your custom field here as well so that value persists in database.
If you are doing it via spro,
Extensions and field personalization ->Configure customer fields -> define customer fields on item level -> Append for Customer Cross-Document Item Database Fields. and add your field here.
Regards,
Karthik Babu.