I check my SEO rank daily and every once in a while it just plain plummets. When it does, it is almost ALWAYS because the SEO plugin failed. When I go to google webmaster utilities, it shows errors with the sitemaps... The sitemaps are gone!
So I go into WordPress SEO, navigate to the sitemap section, checkout the sitemaps... They're gone!
Now all I have to do to solve this problem is hit 'save' and suddenly the sitemaps re-appear.
The problem is that this happens randomly, without any warning. I did not disable/re-enable the plugin or do any other major site changes. I left town for a day, then checked my site, and saw the problem.
Please let me know if there is any troubleshooting I can do to help you with this bug. Love the plugin, just hate having my SEO position drop so drastically!