There is a crucial step missing in the Automatic Generation of the Summary Holdings Statement Based on Items process. The process is documented here:
https://knowledge.exlibrisgroup.com/Alma/Product_Documentation/010Alma_Online_Help_(English)/040Resource_Management/040Metadata_Management/020Navigating_the_MD_Editor_Page?uxp=true#Automatic_Generation_of_the_Summary_Holdings_Statement_Based_on_Items

When items which are linked to the Holdings record are withdrawn, there is no process to update the Holdings record 863/864/865 fields to create an updated 866/867/868 field. When items are withdrawn, the user has to manually edit the Holdings records.

Since the creation of the 863/864/865 field is now automated based on received items being linked to the holdings record, there is a need for the 863/864/865 to be automatically re-created when the linked items are withdrawn.