At 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.”.
To avoid conflicts, the platform deletes the already existing pages from the target SharePoint at the beginning of migration and then recreates 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.
You can delete the URL to the welcome page in the Site Settings-> Welcome page.
Then restart your migration.