Different number of item in Scanning Report and Migrating Report SharePoint online

I had migrated a folder about 50GB from Dropbox to SharePoint online. Then I downloaded report and checked. I saw that there were some items with FullPath in detail scan report not in detail migrate report. And also there were some  items with FullPath in detail migrate report not in detail scan report. Could you please to help me to explain the reason why this issue happen and how to fix this. Many thanks.