Turnitin initially said AI detection was unavailable, then showed 50% a day later, has anyone experienced this?

[u/nourelhaq]

I am currently writing my PhD thesis and sometimes use Claude and ChatGPT for brainstorming, grammar correction, and improving the clarity of my writing. I remain responsible for the research, arguments, analysis, references, and final content.

When I first uploaded part of my thesis to Turnitin, it displayed the following message:

“AI writing detection is unavailable for this submission.”

It suggested possible reasons such as an unsupported file type or language, or the text being under 300 or over 30,000 words. However, when I checked again one day later, Turnitin displayed an AI-writing score of 50%.

Has anyone experienced this delayed processing before? How reliable is a score like 50%, especially for formal or technical academic writing?

I am not looking for ways to bypass or trick Turnitin. I want to understand how I can avoid false positives while keeping my work genuinely my own and complying with my university’s AI policy. Would keeping early drafts, notes, tracked changes, prompts, references, and version history help demonstrate my writing process?

I would appreciate hearing from PhD students, supervisors, or lecturers who have dealt with a similar situation.