The Jira pre-migration checklist states that we should use the query below to find out if our file is valid:
xmllint --noout <Backup File Location>/entities.xml
xmllint --noout <Backup File Location>/activeobjects.xml : 100118
If the command does not produce an output, the file is valid. Any exceptions point to the spot with the formatting error.
The problem is this is essentially a Linux-only option. I looked for xmllint for Windows and I haven't found a simple solution.