Problem

In the beginning of your migration to SharePoint site you noticed the following error:
“The item that you are trying to delete is the current welcome page and cannot be deleted.”.

Cause

To avoid the conflicts the platform deletes the already existing pages from the target SharePoint in the beginning of migration and then recreate all pages entirely. In some cases we didn’t manage to delete one of the existing pages as it is configured as a ‘Welcome page’ of your site. The error is returned by SharePoint, which doesn’t allow the platform to perform a deletion.

Resolution

You can delete the url to welcome page in the Site Settings-> Welcome page.
Then restart your migration.