Office 365 update location is overwritten and attempts to update fail with error code 1603.
ITMS 8.0 HF6
A GPO can control the following registry key which overwrites the Office 365 update URL.
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.
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.