I have the same issue today. No meta box showing (blank) on blog posts. Everything works fine on pages.
I have done a conflict check and it seems to be due to some WPML compatibility issue?
When I create new blog post the SEO plugin is working fine even with WPML activated which is very strange. I posted on Github, hopefully this can be resolved cause there is no way I’m re-writing all of my blog posts…
Thanks
