[miohtama]

Does anyone know the Company A and Company B in the question? Microsoft?

AFAIK public procurement documents are often public.

[srrr]

Searching for "12.1 Regions. Customer can specify the location(s) where Customer Data will be processed within the" (as mentioned in the verdict) yields AWS as the problematic sub-processor for company A: https://d1.awsstatic.com/legal/aws-gdpr/AWS_GDPR_DPA.pdf