Publicize, the part of Jetpack that pushes my posts to Social Mediaâ„¢ has stopped working recently. It turns out to be an issue with the plugin after the last update.
There is a manual fix from the developer.

If you’re comfortable editing files, you’ll need to go to *YOUR DOMAIN*/wp-content/plugins/jetpack/modules/publicize
Open the publicize-jetpack.php file and remove the lines shown here

I removed lines 362-380, saved the changes and now Publicize is working again. I’m sure they’ll include a fix in the next Jetpack update, but this will get you up and running again until then.