I've done a search for blank pages after commenting, and made the following suggested changes:
- ensured no blank lines at bottom of files
- ensured database tables repaired
- upgraded to latest version of core plus plugin
- ensured the form had the required lines.
but the only thing that fixed it was turning off Akismet.
It is sporadic - seems to depend on the content rather than IP address. So if I enter a boring comment by user test, at email@example.com with comment test, that will trigger the problem. Long interesting comments with unusual names usually won't, but enough people have reported having problems, that it needs to be fixed.
So are there any good alternatives to Akismet?
I was looking for wp-spamfree, but apparently WordPress disabled it this week.
If preferable, I'd avoid captchas, and go for pattern matching like Akismet or WP-spamfree, but I'm open to the best suggestion.