Hi maxbstripp, I’ve run into this with isolated stores where another WordPress Theme or Plugin is introducing a rogue ‘space character’ into the file stream while sending the export file to the browser.
This is why you can download the files correctly via Archives (as the export file has been generated and saved to the WordPress Media directory) but not via the Export screen where we load the export file and send it through the browser’s file buffer (and it gets corrupted by other WordPress Themes and Plugins).
