Explanation
Your devices use a service connection point (SCP) object during the registration to discover Azure AD tenant information. In your on-premises Active Directory instance, the SCP object for the hybrid Azure AD joined devices must exist in the configuration naming context partition of the computer's forest. There is only one configuration naming context per forest. In a multi-forest Active Directory configuration, the service connection point must exist in all forests that contain domain-joined computers.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/devices/hybrid-azuread-join-manual