How to fix missing images after an upgrade?
rsync -aviP /home/odoo/.local/share/Odoo/filestore/org_db/ /home/odoo/.local/share/Odoo/filestore/upg_db/
Here `org_db` refers to the backup database before the upgrade, and `upd_db` refers to the upgraded database.
Note: the '/' at the end of the 2 directories is important!