Hi,
Please could you send us a copy of the original backup log? This can be found in the Existing Backups tab of the UpdraftPlus settings page on the original site.
Could you also send us a copy of the migration log? This can be found in the ‘wp-content/updraft’ directory of the destination site.
The contents of the logs will be too long to post here directly, but you can use an online service such as Dropbox or Pastebin, and post the links here. You can also set your reply to ‘private’ if you prefer.
Best Wishes,
David N