Rolling back the PHP version didn't help either.
However, might be unrelated to this plugin...
RESOLVED: I added a 'wejnswpwhitespacefix.php' to the WordPress 'index.php' to clean up that new line at the top of the sitemap.xml and feeds. Started working again, then the update also seems to of worked. Have yet to hunt down where that new line came from, causing the issue.