I've had the same problem. Unfortunately, I wasn't able to find the earlier thread you mentioned, so I'll share the details here instead.
The article I posted yesterday is the only one that hasn't gone out. Most of the time I write the post or copy it into WordPress and publish it the same day. Instead, I saved this post as a draft a few days ago; then yesterday, I just opened it, made a few tweaks, and clicked "Publish." The article posted to the blog, and some of my followers say they received an email update, but most of them didn't.
I wrote up a test post alerting my readers of the problem and published that tonight. It seems like the notifications for this one have gone out successfully.
I'm not sure if the delayed publishing had something to do with the problem. Thanks for your help.
My blog: http://urcpsalmody.wordpress.com/