Office 365 update location is overwritten and attempts to update fail with error code 1603.
ITMS 8.x
A GPO can control the following registry key which overwrites the Office 365 update URL.
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\office\16.0\common\officeupdate
1. Change the GPO affecting the registry key or if the GPO is no longer in use, delete the old registry keys from the following location.
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\office\16.0\common\officeupdate
NOTE: Make an export backup of the registry keys before deleting.
2. Review the GPOs under "Local Group Policy Editor>Local Computer Policy>Administrative templates>Microsoft Office 2016>Updates" for the affected computer.