Course activities copied from an older Moodle version to Moodle 3.0 will need to have the Turitin plugin reapplied.
For example, if you had a course in Moodle AY15 (2.8) that had an Assignment with Turnitin enabled, when that course is moved to Moodle AY16 (3.0), the Assignment in the newer system will not have Turnitin enabled.
Workaround: Reapply the Turnitin plugin to activities you want.
Turnitin with group assignments requiring online text submission
There appears to be a problem using Turnitin with group assignments requiring online text submission.
There are two workarounds:
Use group assignments with file submissions only
Don't use group assignments and keep the assignment submission as online text
Turnitin Document Viewer tool (GradeMark) for entering grades
In rare cases, grades entered in the Turnitin Document Viewer (GradeMark) are taking multiple days (and sometimes weeks) to appear in the Moodle gradebook. There have been a couple of documented instances when grades have not appeared in the Moodle gradebook at all.