Hello
I have the same issue on comments with custom post type.
when a user leaves a comment, you get a white page on wp-comments-post.php
The comment appears in your dashboard, but when you approve it, this comment does not keep the approved state.
The only way I found so far, is to change in the database the comment approved state to ‘1’ but that does not solve the white page after a user leaving a comment !
Plugins I use: Xml sitemap, PHP exec, All In One Seo, WP-Polls.
Ideas are welcomed !