After synced to Office 365 Azure AD cannot be shown in UCA insights:

• The attributes of AD users who are synced to Office 365 / Azure AD cannot be shown in UCA insights. For example:

In Mailboxes - Inventory insight, the "Owner" attributes cannot be shown. "Owner" attributes are the fields under Exchange Mailbox | Owner node.

In the Mail-Enabled Groups - Membership insight, there are semicolons ";" with no proper display names showing in the Group Members field.

Looking into the data source logs: 

Exchange Online Hybrid User Configuration job completed with warnings.

Unable to resolve X users originally directory synced from your on-premise Active Directory forest..

Moreover, there are warnings in Exchange Online Hybrid Mailbox Configuration job as well.

Failed to find on-premise AD distinguished name for X hybrid users...