This scenario usually occurs when the sheet you are trying to import contains headers (the first row of your sheet is headers). In order to solve this, check the ‘Ignore first row’ checkbox at the bottom of the import page.
Note: When leaving the author column empty, the user that imports the file will be set as the author of the imported entities. If you want to change the author value, state an email address or display name of one of the account’s users.