Fix – It looks like your Jetpack connection is broken
unknown_token: It looks like your Jetpack connection is broken. Try disconnecting from WordPress.com then reconnecting.
This problem might happen when you restore your blog from backup. This is not a big problem. You just need to obtain new fresh token from Jetpack site. Easiest and fastest way to do it is to simply disconnect and connect again your site as error message suggests.
Steps below will show you how to do this.
Go to Jetpack / My Jetpack
Click Disconnect site from WordPress.com
Now that you have successfully disconnected your blog from WordPress.com, it is time to re-connect it by clicking Connect Jetpack
Verify that you are connecting as a correct user by looking at the Connecting as: field. If everything is ok, click Approve button
Done! You should get confirmation screen as shown below. Now Jetpack should work with no problem.