“Jetpack could not contact WordPress.com: register_http_request_failed.”
After reading posts online like this one: register_http_request_failed … SSL connection timeout (WordPress forums) I realized that the issue was in fact an SSL connection timeout from your WordPress host to the Jetpack server. In my particular case it was a firewall issue as the Jetpack server did not pass the https validation. My guess is that back in the day Jetpack used the wildcard certificate from WordPress and as it had a WordPress.com domain there were no problems. Right now if you visit: https://jetpack.wordpress.com/jetpack you´ll see that Jetpack has the Jetpack.me domain and that it uses the *.WordPress.com certificate. The firewall on my web server then noticed the mismatch and threw the error above. After adding an exception to this certificate things worked again.