Anyone else seeing these and knowing more about how the transfer of
such personal data happens between those partner and what kind of
partners those are?

This is usually easy to find out with a data information request.
I send such requests regularly, mainly as soon as I receive email newsletters of Swiss companys or offline post. Below are a few stories about how my address and e-mail data regularly change hands. Making sure that doesn't happen is very difficult.

First Story, 2016:
Second Story, 2017:
Third Story, 2019: