You have several options for upgrading or migration. It is not an easy task:

1. Upgrade Odoo with the official API. It is not for free. I have read on the website that the main steps are:

   • Creating a request
   • Uploading a database dump
   • Running the upgrade process
   • Obtaining the status of the database request
   • Downloading the upgraded database dump

2. OpenUpgrade. It is a migration tool, but it works only for the modules specified on the website.

3. ETL tool such as Clover ETL. Maybe too much work

4. Migrate specific tables by exporting them in a CSV file and import them back to the new Odoo version. This is useful if someone want to start from scratch, you will only need to import the main tables.

5. Use the flag --update=all. You say that you have used this way after upgrading Odoo to the version 9, but I do not recommend it. Even if you don't change the Odoo version, if you update all the modules at the same time you will have a high chance to get several errors. It is like the Openupgrade method, but it is worse because you do not take into account the migrations folder where all the migrations scripts are stored such this one, just an example.

NOTE: And if you have programmed a custom module you must migrate it to the new version before the migration. If you have many custom modules the migration would be more expensive.