Hello,
I've reproduce the same scenario and checking the field location_id in stock.lot.
(lot.location_id = quants.location_id if len(quants.location_id) == 1 else False)

The “Location” on a Lot/Serial Number does not show the real-time stock location.But after you do a partial delivery, internal transfer, or any stock movement, Odoo internally splits the stock into multiple records (quants).

Even if the remaining quantity is still inside the warehouse, Odoo can no longer assign a single location to the lot.

Hope it helps.

Hi,

The issue where a lot's location changes to "None" after a partial stock move in Odoo, even when units remain in the original location, is likely due to incorrect location tracking, configuration issues, module conflicts, or a bug in Odoo.

To troubleshoot, check your Odoo configuration, examine the stock moves, test with a new lot, disable custom modules, and review Odoo logs. Possible solutions include correcting location tracking logic, adjusting configuration settings, resolving module conflicts, or applying an Odoo patch. If you can't resolve it yourself, contact Odoo support or a partner.

Hope it helps