Can't login - unexpected response, single sign on failed

Up to 12 hours ago I was playing Runescape on Steam just fine. However, just now when I booted it up, I get an error telling me single sign-on failed. Clicking on the "continue" button led me to another error: Runescape received an unexpected response (25). Please try again later, or check the Runescape website for server maintenance.

And then it loops through these errors when I click "Try Again".

Sorry for the low quality, stackexchange upload limit is 2 MB.

Things I have tried:

• Uninstall -> Reboot -> Install
• Verify integrity of game files
• Setting launch option to runescape
• Clear cache

I just tried the standalone client and it works; however I only want to play on Steam as it has the steam overlay and integrated voice chat through that.