Looking at each one, the error seems to always be one of three pages. The login page (per my original message) or one of two different blog pages.
What is odd is that these are really old blog posts from back in 2012. So it's not like customers are hitting those pages on a regular basis. I'd be shocked to learn that ANYBODY is actually visiting those pages today. Much less, several times a day.
And I can visit those pages and it does not generate an error log entry when I do. Just like I can login without generating any errors.