Tizz on "[Plugin: WordPress SEO by Yoast] 404 Error when trying to create a sitemap"

For me this worked: disable the sitemap feature by unchecking the box, save, and then check on again. Now maps are visible.
Conclusions that I have drawn after repeated experiences of this kind: after any update or upgrade or big modification check the Yoast sitemap, because it's not stable or reliable.
In these cases, might works:
1) Click save in the sitemap's page settings
2) Click save in the permalinks plugin page settings
3) Disable the sitemap feature, save, and then check back