404 error

The first thing to check is whether any other plugins on your site may have a conflict. Please check our Known Issues list here:
http://jetpack.com/support/getting-started-with-jetpack/troubleshooting-tips/

You can also try to deactivate all plugins on your site before publishing your next post, and see if that resolves the issue. If it does, then activate them one at a time to determine which is causing the conflict.

If that doesn’t help, please rule out a theme conflict by temporarily changing your site’s theme to a default theme (such as Twenty Sixteen) and trying again.

Please let me know how that works for you, and we can go from there!