When you create reports and other changes in multi company environment there are a couple of things that you should pay attention to:

1. If you want to create addresses or get information's from the own company don't use "res.company". That is not the right field and will give you wrong outputs even though sometimes it seems to be right. Use "doc.company_id"/"o.company_id" instead.

2. Always work in System language when you do changes. Otherwise Odoo will change the standard value in the value of the translation. For multi company with different languages that can get very problematic.

3. Keep in mind that each change in Studio will be there for all companies. Therefore if you need to hide sth. make a domain depending on the company -> therefore check 1.