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Similarity reports may be slightly delayed if Turnitin goes down; however, Moodle will keep automatically resubmitting the paper until service is restored, at which point the similarity report will be generated and sent to Moodle. No further action will be required in Moodle to make this happen.
If you are experiencing problems with the generation of similarity reports, please consult our guide What to do when Turnitin doesn’t generate a similarity report?