One comment per post, no error – just blank page

My comment section (https://bligbi.com) hasgone wacky this morning. Apparently if anyone, including me, tries to comment on a post that already has a comment, they get a blank page (wp-comments-post.php in the address bar). I haven’t changed anything within the last day or more so I can’t figure out what happened.

On a related note, the notifications for new comments ceased when I updated a couple of weeks ago. It’s not a big deal, but it is annoying.

I’d appreciate any help that can be offered. Thanks.