Situation:

You have setup the SCCM Hybrid MDM with Microsoft Intune by following this guide:
https://docs.microsoft.com/en-us/sccm/mdm/deploy-use/setup-hybrid-mdm

But you cannot have your Hybrid MDM polices to be deployed on mobile devices. You checked the Cloudusersync.log log, it says
“Starting user delta sync, raise failure status messages = True”
and there is no any user has been synced (number count is all zero).

/!\ Note:
If it works / worked, you may still see the message, but the count number is not all zero.

Analyze

To have the Hybrid MDM with SCCM + Intune work, you must meet the following requirements:

• Service Connection Point must be enabled and be online mode
• User UPN must match the one on Cloud, do one of the followings:
• xxx.onmicrosoft.com – add this to “Active Directory Domains and Trusts” – “UPN Suffixes”, or
• Add company domain to Azure AD

For demo environment, do not forget to setup the UPN, as following:

References

[1] Setup hybrid mobile device management (MDM) with SCCM and Microsoft Intune
[2] Confirm domain name requirements with System Center Configuration Manager and Microsoft Intune