I’ve gone ahead and moved your post to its on thread to better follow-up on your issue.
I believe tasks aren’t uploaded in the same order as in your CSV because you have them nested in Sections. In the preview, they remain in the correct order because the section are materialized in a column, while in Asana they display in Sections.
So when uploading your tasks to Asana, the CSV importer creates your new sections, and nest each task under the section you have selected. Hope this makes sense 
Technically, I don’t think it is possible for the CSV importer to nest tasks under the Sections you’ve selected and list tasks in the same order than your CSV, but I’ll go ahead and make a note of your feedback to our team.
I’m aware this doesn’t solve your issue, but it hopefully helps clarify why this is happening! Don’t hesitate to reach out if you have any follow-up questions 