Hi Tom Esker,
The behavior you are seeing on both the domain-joined and the problematic non-joined system stems from a conflict between the activation channel (your Microsoft Account/Consumer ESU subscription) and the update authority (how Windows is configured to look for updates).
Since you are using a Microsoft Account to manage these licenses (rather than a Volume Licensing MAK key or Azure Arc), you are effectively using the "Consumer/Small Business" ESU path. Here is how to fix both:
1. The Domain-Joined System (Stopped working after 1 month)
The error "Your device is no longer receiving security updates" on a domain-joined machine is almost always caused by Group Policy overriding the activation check. Even if you signed in with your MSA, a domain-joined PC usually has a Group Policy setting pointing it to a local WSUS server (or SCCM) for updates. When the PC checks for the ESU entitlement, the "UseWUServer" policy forces it to ask your local server instead of Microsoft's public servers. Your local server doesn't know about your personal ESU subscription, so the check fails, and the license drops.
To fix, you must tell this specific machine to bypass the local WSUS server to validate its license.
Open Registry Editor (regedit) as Administrator. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
Look for UseWUServer. Change it from 1 to 0. (Or delete the key). Restart the Windows Update service (net stop wuauserv then net start wuauserv). Go to Settings > Update & Security > Activation. It should re-sync the entitlement against the public Microsoft servers.
2. The Non-Domain Problem Machine (Never worked)
The fact that you deleted it from your Microsoft Account devices list and "it is not getting automatically added back" is the smoking gun. If the device does not appear in your cloud portal, the hardware fingerprint has not been registered, so Microsoft refuses to send the ESU license to it.
- Root Cause 1: Telemetry is Disabled The "Consumer ESU" requires a minimum level of telemetry to validate the hardware ID. If you used a privacy tool or script to "block spying," you broke the ESU registration.
Check Registry: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\DataCollection
Ensure AllowTelemetry is NOT set to 0. It must be 1 (Basic) or higher.
- Root Cause 2: The Sign-In Assistant is Broken The service responsible for syncing your machine to account.microsoft.com is likely disabled.
Open services.msc. Find Microsoft Account Sign-in Assistant. Ensure it is set to Manual or Automatic and is currently Running.
- Root Cause 3: Missing the "Preparation Package" Just having "all updates" isn't enough. There is a specific, separate patch required to trigger the ESU client code.
Verify you have installed the Licensing Preparation Package for Windows 10 ESU (KB5001716 or newer variant). Without this specific KB, the OS doesn't know how to consume the subscription.
3. How to verify if it worked (The "Truth" Command)
Don't rely on the GUI. Use the command line to see the actual license status. Open Command Prompt as Admin and run: slmgr /dlv
Look for a section named "Windows 10, ESU-Year1..." (or similar Add-on).
If it says "Licensed": You are good.
If it says "Notification" or "Unlicensed": The handshake failed.
If the section is missing entirely: The Licensing Preparation Package is not installed.
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to ACCEPT ANSWER. Should you have more questions, feel free to leave a message. Have a nice day!
VP