Pingbacks stopped working?

Hi there,

I recently switched from WordPress.com to www.remarpro.com (hosted on HostGator), about 3 weeks ago. A few days ago, I noticed that my posts were not generating pingbacks on other blogs and web sites that I’d linked to — even ones that used to accept them.

So I tried pinging older posts of my own to see what would happen, and it mostly worked (with ONE weird exception in which, for whatever reason, that particular post would not get pinged, no matter how many times I published a post linking to it). I always publish my posts with the box checked for allowing pingbacks and trackbacks, and I have both boxes checked in the Settings > Discussion page relating to pingbacks/trackbacks as well.

Strangely, I can still receive pingbacks from links on other people’s blog/sites, though. I’m wondering if the problem occurred after installing some plugin recently, so I experimented with certain ones deactivated but to no avail so far. I’m running a child theme of Twenty Twelve (no significant changes from the parent theme) at https://www.jaypinho.com, with the following plugins activated:

Akismet
Categories to Tags Converter Importer
Co-Authors Plus
Editorial Assistant by Zemanta
Insert Headers and Footers
Jetpack
Upload Media for Contributors
upPrev (inserts a NYT-style slide-in tab towards the bottom of the article with link to previous post)
WordPress Importer
WP Super Cache

Anyone have any ideas? Thank you so much!

Jay