Problem: The Date Modified field for all content in Portal for ArcGIS is changed following an upgrade to ArcGIS Enterprise 10.6
When upgrading ArcGIS Enterprise to version 10.6 from earlier versions, the Date Modified field for all content in Portal for ArcGIS is altered to the date when the upgrade was performed.
This is a known issue. This occurs when upgrading to Portal for ArcGIS to version 10.6 on all supported operating systems. It has been documented as a software defect BUG-000112885, and has been addressed in ArcGIS Enterprise 10.6.1.
Solution or Workaround
For customers who have already upgraded to 10.6, reverting to a backup of the previous version returns the Date Modified field to its original values. Customers who rely on the Date Modified field for their workflows should be mindful of this behavior when planning an upgrade. This issue occurs when upgrading to 10.6 from all previous versions of Portal for ArcGIS.