This from Turnitin at 20:00 on the 12th of August:
We’ve fixed it!
Due to an unexpected third party intermittent service degradation, users of Turnitin, Turnitin UK, & iThenticate may be experiencing sporadic network issues while trying to use the service.
We are pleased to advise that the service has been restored.
We encountered a degradation between the following times:
BST August 12th 18:10 – August 12th 19:06
Please accept our apologies if you were impacted by today’s degradation”