Thanks for reaching out to Microsoft Q&A.
First, I'd advise you to make sure the connection between the Entra Connect server and Entra endpoints is ok by using the command: Test-MicrosoftEntraConnectHealthConnectivity -Role Sync.
In case there's no connectivity issues, try re-registering the agents by using the command: Register-MicrosoftEntraConnectHealthAgent -AttributeFiltering $true -StagingMode $false
Both commands and more information about the Entra Connect Health agent can be found on this documentation: https://learn.microsoft.com/en-us/entra/identity/hybrid/connect/how-to-connect-health-agent-install
Let me know if that's helpful to you.
Thanks,
Fabio