Problem

During migration from and/or to SharePoint sites, you have noticed a following error:
” FATAL_ERROR for site [Name of the site] : Cannot connect to the parent site [url of the site].”.

Cause

The [Name of the sites] was checked-out to one of the users for editing purpose and the platform can not connect to it.

Resolution

Ask your user to check-in the impacted site and publish his/her modifications. Then restart the migration.

To check, by whom the site was checked-out, go to this site and check the information message:
Site checked-out to user