Thank you for posting and using GroupDocs.Comparison.
Could you please specify which the Comparison product you are using: Cloud or .NET.
Also will be useful if you share with us your files that you tried to compare and we will investigate it . If you use the GroupDocs.Comparison for .NET, then please specify its version.
Please come back to us with these details and we will be glad to help you.
Your Document Collaboration APIs
Follow us on LinkedIn, Twitter, Facebook and Google+