Go to the Performance > Browser Cache menu of the W3 Total Cache (W3TC) Plugin. Then disable Do not process 404 errors for static objects with WordPress. You should now be able to view the sitemap in your browser.

Go to the Performance > Browser Cache menu of the W3 Total Cache (W3TC) Plugin. Then disable Do not process 404 errors for static objects with WordPress. You should now be able to view the sitemap in your browser.