This from Turnitin at 20:00 on the 12th of August:

“Incident resolved

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”