Azure AD sync issue

Hi,

Have abit of an issue at hand.

We recently aquired a contract with a new company. We are in the process of migrating all their data over to our datacenter.

Issues
What should be done and what have happened.

The existing company had an tenant in O365 with Azure AD connect running. All users from their local AD appeared in O365 for SSO.

I set up an Azure AD connect that is running through a proxy in DMZ.

When we reached the cutoff time, and started to move all their stuff to our datacenter we got an issue.

ADFS is reconfigured to use our system and our ssl token certificate
The Azure AD service is running.
Local AD is set up and have the same UPN name as existing UPN in O365 tenant.
Azure AD services report success for connection and synch to O365.
In the Full import i notice that all the users appear as deleted and not added.
In the O365 it sync still towards the "old" sync server.

As of now it seems the sync appear to start fine and somehow reports that the users will be deleted before reaching the O365.

So some questions :

Is there some logging (or where to find) for the sync it self and why it deletes the users before O365 ?
Is there some O365 settings to specify where the sync should be ?

All hints and tips are extremely welcome........