Contacts are always being switched back to non-marketing contacts

Contacts are always being switched back to non-marketing contacts

Hey there.. 
hope someone can point me towards the one button, I need to click ;-)

In Marketing Automation 2.0, I setup the integration from CRM to Marketing Automation 2.0 (MA2.0). So far so good. 
Contacts and leads are being imported to MA2.0

They are being marked as "Subscribed to Marketing topic - Consented"
Thats how it should be. 

Before I send out a newsletter, I checked the total number of recipients - which seemed rather low. 
I saw that a lot of my contacts in MA2.0, now get automatically tagged as Marked as a Non-Marketing contact

Which field / button in CRM is driving this behaviour? Or ist it in MA2.0?

Hope someone can guide me here...
Looking forward,
Ajay.