Nope, I tried removing HOME/.lighttable with LT turned off, it got regenerated back upon restart and I'm getting the same error.

I'm behind a proxy; not sure if it makes a difference.

Ah, the proxy is probably it. Does your proxy bypass 127.0.0.1?

Quickly scanning the configuration, looks like it does. I've tried temporarily disabling the proxy in Control Panel, but no luck; I'm not sure this is the correct way to override proxy settings for Light Table, though. Where does it pick its proxy settings from?