HI everyone, i was wondering if someone knew how the Exchange 2013/O365 Hybrid mechanism works.

In my particular case I have AADConnect configured to use the ms-ds-consistencyGuid as the sourceAnchor (selected in the wizard during install). While the users are added on AAD and available in O365. Users can login to the portal and that all seems to work.. (given users have ms-ds-consistencyGuid filled). O365 users can even login to their mailbox...
However, it seems the on-prem exchange does not recognize any O365 mailboxes. In a default scenario, the O365 mailboxes should be added to the ECP Mailboxes overview with O365 as the location for the mailbox..... and the properties of an O365 mailbox user should be changed to recipient type=-2147483642 or something..  and as Exchange does not see the O365 mailboxes, no contact/mailenabled user is created as a result.. and thus no mail flow
In my AAD Connect sync I see that only an x500 and the msDS-ExternalDirectoryObjectId is replicated back to on-premises Active Directory.
(ProxyAddresses: x500:/o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=blablablabla)
(msDS-ExternalDirectoryObjectId: User_b153abb8-e353-422f-blablablablabla)

Nothing else seems to be replicating back/forth..

I even managed to migrate a mailbox to O365, but even that one does not replicate or change .. so according to ECP (On-Premises) the mailbox is still on Exchange 2013 (CU8). while the migration wizard claims a successful migration.
is there another process inside Exchange that manages this? is it additional code in the AAD Connect that does not work? Which component is responsible for assigning the msExchRecipientDisplayType and msExchRecipientTypeDetails and other attributes?