The issue you are encountering with changing the default source location in one PoS and it affecting other PoS is likely related to the fact that you are using the same database for all your locations.

Odoo uses a shared database by default, so any changes made to one instance of the Point of Sale will affect all other instances. This means that when you change the default source location in one PoS, it will affect all other PoS instances that are connected to the same database.

To address this issue, you can create separate databases for each location. This will allow you to configure the Point of Sale for each location independently, without affecting the other locations.

To create separate databases for each location, you can use the Odoo multi-company feature. This feature allows you to create multiple companies within the same Odoo instance, each with their own set of data and configurations.

Once you have created separate databases for each location, you can configure the Point of Sale for each location independently, including setting the default source location for each PoS.

Regarding your question about using different locations instead of different warehouses, this should not be related to the issue you are encountering. Both warehouses and locations can be used to track inventory, and the important thing is to make sure that each product is assigned to the correct location or warehouse, and that the default source location for each PoS is set correctly.

1.Go to Inventory> Configuration> Locations.
2.Create a new location for each PoS system you have.
3.Go to Point of Sale> Configuration> Point of Sale.
4.Edit each PoS system and set the Location field to the corresponding location you created in step 2.

Configuration settings: Look for options or settings that allow you to specify which PoS terminals or locations should receive updates or changes. Some systems have options to apply changes selectively or exclude certain terminals from synchronization.

If all your PoS systems are using a shared configuration file or database, changing the default source location in one system might inadvertently update the configuration for all the systems. Check if there is a shared file or database that controls the default settings and ensure that it is not being overwritten or synchronized across the PoS systems.