The Checkstyle plugin is producing invalid output due to invalid characters in the output XML.
<error message="This VI's front panel alignment grid size (10) does not match the user specified size (12). You can configure the front panel alignment grid size in the <b>VI Properties > Editor Options</b> dialog box." severity="info" source="Alignment Grid Setting"/>
You can see that the > is being escaped correctly, but the HTML bold tags and are not being escaped.
These characters should also be escaped, or the html tags removed.