@patrickgowp This issue occurs when another file, plugin, or theme adds additional code to the beginning of the sitemap file. You will need to view the source code of the document in order to confirm this, and we have additional information on this and how to resolve this error at the following link: https://kb.yoast.com/kb/xml-sitemap-error/.
We would recommend running a conflict check to identify whether another plugin or theme is adding the additional styling information in the sitemap file. The fastest way to do this is to deactivate all non-Yoast plugins and switch to a standard theme like Twenty Nineteen. Test this on your development or staging site, if you have one. If not, we recommend using the Health Check & Troubleshooting plugin which can be downloaded here: https://ww.wp.xz.cn/plugins/health-check/. This plugin allows you to run a conflict check without affecting normal visitors to your site. If you are unfamiliar with checking for conflicts, you can find a step-by-step guide that will walk you through the process here: https://kb.yoast.com/kb/how-to-check-for-plugin-conflicts/
Thank you!
After investigating, the plugin “Gravity Forms Styles & Layouts” seems to be the cause of the sitemap issue.
We’ve disabled it and the sitemaps are working now.
Thanks for your reply and confirming you were able to resolve the issue by disabling the Gravity Forms Styles & Layouts plugin. We’re going ahead and marking this as resolved, but you’re always welcome to re-open the topic.
