Microsoft 365 Apps admin center devices are not checking in.

A few quick things I'd look into:

Diagnostic data settings. If your GPO or Intune policy sets Office diagnostic data to Off or Security instead of Optional/Required, the portal won't see those endpoints.

Network rules. Make sure your firewall or proxy isn't dropping traffic to *.config.office.net or *.officeconfig.msocdn.com. The onboarding fails silently if those endpoints are blocked.

Tenant group assignments. Double check under Cloud Update settings to see if your target device groups are properly assigned or if there's an active exclusion policy blocking those 27 machines.

Keep in mind that even after fixing telemetry or network access, it usually takes 24 to 48 hours for devices to report back to the portal once users launch an M365 app.