It seems that I have the same issue; I'm running a server on a local (or local network) machine and when I make a http connection with it Safari randomly doesn't load resources (such as css or svg files). Sometimes it even doesn't load the main page. I don't see any errors in the console, just randomly closed connections. Rico's answer seems to assume the resource is local to the app, while my (and I assume rastislavliptak's) issue is with files hosted on a local server.