My gut says this is CloudFlare’s problem, but apparently they only provide support to customers (you), so if this is indeed a CDN problem you may have to escalate to their support.
My HTTP connections to derpicdn frequently drop, usually when long responses are involved. If SPDY/HTTP2 is enabled, the problem is exacerbated because, AFAICT, the entire session and all in-flight requests are aborted. This manifests as missing thumbs or partially loaded images.
Is the server or the CDN configured to abort slow transfers? Unfortunately, I only have 768kbps, and loading a full-size image or two while browsing thumbs can result in a lot of parallel requests. AFAICT, the browser parallelizes the requests for all thumbs of a result page.
Disabling SPDY improves things quite a bit. Perhaps because parallelism is reduced, so requests are completed more quickly. Perhaps because only one request is lost if the server aborts a connection, because requests do not share connections.
I’m also puzzled by some images starting to load uninterlaced, getting interrupted, and upon attempt to continue loading them (right click -> view image) getting a “corrupted content” error. On reload, they load as interlaced images.
Mozilla/5.0 (X11; Linux x86_64; rv:46.0) Gecko/20100101 Firefox/46.0
Out of curiosity, how does the H2 setup work, anyway? Does the CDN handle it all and your server only sees a bunch of (persistent) HTTP 1.1 connections?