It could be a bum DNS or content filtering. Yes, you didn't ask for a solution but I'm going to share what I would try next. The symptoms are consistent with country or ISP meddling.

1. A VPN. Install Opera, turn on its free VPN and see if the problem vanishes. If it does, it's your ISP or a firewall like China has.
2. Bum DNS. Google "How do I change to the Google DNS?" Change that and test.