You submitted a paper which contains significant portions of text taken directly from certain sources. However, Turnitin did not highlight these as similar*.
Turnitin's similarity checking is only as good as their database or index of the web.
As new sites and pages turn up every day, Turnitin may not have indexed the page or the site yet.
Please refer to Turnitin's documentation on this topic.
You can send a support request to Turnitin to ask them to expedite adding the web site(s) or web page to their database.
* Some users have said that Turnitin does not highlight plagiarised text. This is not accurate because Turnitin highlights similarity. Only a human determines if there has been an instance of plagiarism.