I've done a great deal of digging (here on the forums and all over Google) on this problem and am coming up with nothing.
I noticed two of the pages on my site went blank after I edited them a couple of months ago. I knew at the time that I had a theme installed that hadn't been updated for over a year. The sheer size of the site meant a huge project to change the theme, which took a while. I found out about the theme having been abandoned not long before this, due to the fact that I was seeing some "odd" behavior from the site, generally. I knew, in other words, that I had some problems to fix.
About a month ago, I installed a new theme, reviewed all of the plugins, reducing the number and swapping out better options, improved the .htaccess file for security and speed, and optimized all of the images. I cleaned up the database by targeting files left over from old plugins and themes that didn't get removed by uninstalls and setting revisions to 3.
The site is functioning well so far, with speed tests going from ~47-50% to 90-95%. My goal is a consistent 95% or better, but the site is getting "hit" in the scoring a bit for sporadic server slow downs, which I know are associated with the brute force attacks that have been ongoing. The last bit of stuff I was going to do was thoroughly examine whether I've got 404s and fix them and investigate how many jquery plugins are loading their stuff in the header rather than the footer.
I'm sure I've overlooked something in cleaning up and improving, but I can't imagine what could be associated with this page issue.
Although things are generally working well, the problem with the two blank pages that I had when the old theme was installed has not gone away as I'd hoped and I find that any page I edit displays blank after they are updated, just like before. I have a lot of pages and a good many of them need revisions. So, besides the obvious problem with those that are blank, I'm frozen in doing anything to the others until I sort this out.
To narrow down the potential cause(s), I deactivated all of the plugins on the site and installed View WP Error Log (http://wordpress.org/extend/plugins/view-wp-error-log/) and then visited various locations on the site, including the blank pages and other, working pages.
I got one error message associated with one of the plugins that appears unrelated (parse error, unexpected t string), although I can't be 100% sure. It does bother me that an error would show even with the plugin deactivated:
PHP Parse error: syntax error, unexpected T_STRING in /home/usr/public_html/wp-content/plugins/code-snippets/code-snippets.php(1090) : eval()'d code on line 6
All I can come up with at this point is that the previous theme somehow damaged pages in the install - whether it'd be in the database or WordPress core, is over my head.
The author apparently decided to abandon the theme after his last update was rejected with a long list of changes required by the reviewer before it would be accepted. http://themes.trac.wordpress.org/ticket/5904
I can't tell from reading the review which, if any, of the problems listed by the reviewer would cause changes to the install regarding pages, but the rejection seems relevant.
I don't know where to look to figure what is the causing problem. Any insight would be appreciated.