Some update files aren't signed correctly. Error code: (0x800b0109)

Question

Suddenly most of my domain machines get this error when checking for updates against local WSUS Server

Answer 1

Kindly go through the following Microsoft reference article:

Troubleshoot issues with WSUS client agents

• Check WSUS Server Connectivity Ensure that your WSUS server has proper internet connectivity to download update files from Microsoft's servers. Verify that there are no network or firewall issues blocking the download of updates.
• Make sure that the WSUS server has successfully synchronized with Microsoft's update servers. Go to the WSUS console and check the synchronization status. If there's a problem, try manually initiating a synchronization to see if it resolves the issue.
• Stop the WSUS service and delete the contents of the SoftwareDistribution folder (located at C:\Windows\SoftwareDistribution on the WSUS server). Afterward, restart the WSUS service.

Answer 2

Did you recently make a change in the SSL Certificate? - Ensure the certificate's root is trusted by all systems

https://www.ajtek.ca/wsus/how-to-setup-manage-and-maintain-wsus-part-7-ssl-setup-for-wsus-and-why-you-should-care/

Answer 3

Solved

after doing this

HKLM, then Software, Policies, Microsoft, Windows and finally Windows Update.

and Restarting BITS and Windows Update Service internal WSUS starting to the machine