In the last month (or so), at least two of my feeds have disappeared (minimum, there might have been others that I haven’t noticed) .
The XKCD feed was my first to go, and it was probably a month before I noticed it was even gone. I re-added it manually. This was at some point around a month ago.
Just now though, I realized my MacRumors feed was gone. It was definitely there within the last fews days.
It’s not the end of the world, but thought I should point it out.
I fixed the bug where XKCD disappeared (I also re-added it for everybody affected). But the Macrumors bug is new. Can you share the newsblur.com url of the feed?
It looks like this is the correct feed: http://www.newsblur.com/site/5986322/macrumors-mac-news-and-rumors-all-stories
I’m not sure what happened. The only way a feed can delete itself is if it explicitly merges into another feed with a redirect. That happens occasionally (by accident on account of the publisher), and the bug fix I introduced was to ensure that the feed would be redirected 20 fetches a row before it was committed.
Mac rumors would have to redirect itself 20 times in a row for it to delete itself, which is a possibility.
I’m honestly not sure how to find the Newsblur URL for it (MacRumors doesn’t have all of the feeds showing on their website that they used to before they ditched vBulletin a few months back). When I just added their feed they advertise on their site now (http://feeds.macrumors.com/MacRumors-All ) it gives me this one: https://www.newsblur.com/site/5990677/macrumors-mac-news-and-rumors-all-stories but I think that’s the wrong one. It only has 37 followers; I’m almost positive the one I had before had lots of subscribers. If I knew how to search for them, I’d try to find the right one. But I might just be crazy here anyway.
Side note, I didn’t just get a new XKCD feed (probably because I’d already manually re-added it), but I see the What If feed just showed back up. I hadn’t even noticed that it was gone yet. Thanks for that 
I think you’ve essentially got 3 that need to be merged right now. Just clicking on subscribe on the bottom of the page for that feed, I get a popup with 3 versions of that feed from you, one with ?format=xml, one in all lowercase, and one with title case.
I would be willing to swear that it had more subscribers than even all 65 of those combined, but I guess I’m wrong.
When I get home, I’m going to look on my desktop for my old Google Reader export from when I switched to Newsblur, and I’ll try to find their old feed URLs. They used to offer more than this one. Maybe they are redirecting around now.
I just experienced this issue with RSS feeds for reddit as well. They disappeared while I was using the iOS app approximately 10 minutes ago.