Unfortunately the Jetpack developers have confirmed that we are unable to troubleshoot this any further on our end. Internal server errors are host-side issues that can’t be solved without knowing the cause, which we can't do without seeing your error logs. If your host won't provide them or help you figure out what's causing the server error, you might want to consider switching hosts if Jetpack is essential for the site.
I'm very sorry we couldn't resolve this for you.