Articles I've written
ERR_SPDY_PROTOCOL_ERROR, and an invalid HTTP header
When migrating your site to a more performant HTTP/2 protocol, it may happen that Chrome will not load a page and will display This site can’t be reached with
ERR_SPDY_PROTOCOL_ERROR instead. HTTP/2 is derived from the earlier SPDY protocol, that's probably why the error message doesn't mention HTTP/2 at all.