WORKAROUND
To find the missing files you could traverse ('Show Content) down through the relevant Sharepoint site directory structure in the ODM UI dashboards, like in the attached document. Each level with show will shows its type (Site, Web, List, etc.), its URL location, and number of source items and number of target items. where the target number is smaller, that ought to be one of the places a file(s) got missed in the migration. And those details on files can help you to find the location of the files that had been missed in the migration.
STATUS
Enhancement request being evaluated by product team for possible implementation in a future release of ODM.