I’m getting these same errors too, on a fresh install. I have cloudflare for my root domain, but it’s bypassing on the subdomain I’ve installed discourse to https://forum.theopen.institute. I followed the instructions here for running other sites on the same machine.
The strange thing is, each time, I am able to get most of the way through the welcome and installation process before I start getting the ERR_SPDY_PROTOCOL_ERROR responses in console.