A date and time-stamped Site Sync Log list is created every time a design sync is ran. The list will be displayed after a sync if anything was written to the list.
The items written to the Site Sync Log are grouped according to severity:
This details items that the sync was unable to copy.
This details possible changes that were skipped due to the selected design sync settings.
This details the major changes that were synced such as adding and deleting lists and columns.
You can configure the items that are included in the log on the Sync Design page.