Hi there,
Yep, had the same problem. Turned WordPress upside down,didn’t find anything.
My solution was to check the firewall. I’m running with 2 internet lines (different providers) behind a Kerio Control (hardware firewall).
NAT is turned on, translates public IP addresses to internal IP addresses. Because JetPack is phoning home, I needed to turn on enable “source NAT”, too, to make sure an outgoing connection (from this server) is using the same public IP address as the incoming traffic (for this server).
Greetings,
Peter