You've encountered a "feature" of the Windows Update installation system related to logon type of a PowerShell Remoting session (Invoke-Command, etc.). The creator of the PowerShell Deployment Toolkit (PDT) found a different workaround which involves scheduled tasks and explains why it does not work in below video from TechEd North America 2014. Watch the complete video or jump in at or before 00:28:57.
Last but not least. The CcmExec process is the System Center Configuration Manager (SCCM) client which would be a better solution than using PsExec to install Windows Updates. If you have access to SCCM system or can ask someone to package the updates and deploy them for you.