I checked your site connection and everything seems to have been synced properly so it should be working for you. Can you try these steps to troubleshoot your problem?
1. Disable all other plugins, then checking to see if the Related Posts displays. If it starts working properly, turn your plugins back on one-by-one until you see them disappear again. Then note the plugin that caused this error and get in touch with us. Sometimes Jetpack and other plugins are incompatible; just let us know and we’ll see what we can do.
2. If the plugin step above doesn’t help, try activating Twenty Fifteen (one of the default WordPress themes) temporarily as your theme. Then check again. If it starts working, likely something in your theme is broken and you should get in touch with your theme’s author.
If you’re still having the problem after following these steps, please let me know and I’ll be happy to look into this further for you.
Let me know if you have any questions.