For the first time in ages, KF is unstable for me on Tor today.
I can archive .onion pages just fine right now. Usually when the .onion is getting DDoSed, archive.is either can't archive pages at all, or it doesn't load Null's comments when it archives them only partially. Here's what that looks like. This is how I'd check if KF is getting DDoSed without actually visiting the site.