Thanks Martin. The problem seems to lie with our company proxy (which requires authentication). I have tried retrieving the page on another network with a transparent proxy, and it all works fine. Unfortnately, any https page I try to retrieve on the company network fails in this way with after a long period of inactivity. However, I can retrieve the page using a standard browser through the same company network. I think there must be something weird going on with our proxy server.
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