Have you tried reuploading this image, and do you get the same error each time?

Man I know this is like a billion years late, but I finally got around to looking into this. First, I tried uploading that file myself, and did not get the same error. So the next step was to research it a bit. You didn't mention your browser, but I found out this is a Chrome-specific error message related to some internal Chrome things.

It seems to be a rare occurrence, but if you run into it again, I found this article (offsite) which has some things you can try to resolve it. https://switchgeek.com/err-spdy-protocol-error/

(And here (offsite) is the Chrome bug report on it, though it appears to have been closed without being fixed due to how rarely people run into the issue.)

So... tl;dr I'm afraid this is something on the browser's end, and there's not much Subeta can do about it. I hope this information is helpful at least. And apologies once again for letting this report sit for so long ;;