Been playing around with this more. The Spider Pennon big picture wasn’t loading as well as The Tinker’s thumbnail image. Chrome Dev Tools definitely say that the files can’t be loaded by the server. If I locate the file in the Network tab of the tools, I can see the error. I have the option of opening the file in a new tab. If I do this, there’s a brief error saying the file can’t be found, but then it loads.
After this, if I reload the webpage, the icon loads just fine. If I had to guess, I’d say that there’s something happening when the file is downloaded, but I have no idea what that might be.