According to Newsblur UI, the Cloudflare Blog (https://blog.cloudflare.com/rss/) returns HTTP 503 only. If I try it with curl from my machine, I get a proper 200 with content that validates on validator.w3.org. Also, direct fetching from validator.w3.org works as well.
I have no idea what Newsblur could be doing differently to cause the 503. Maybe some blocking on Cloudflare side? @samuelclay, can you see some more helpful details in the response directly on your servers?
I worked with a couple folks at Cloudflare about a year ago to get NewsBlur placed on the allow list. That seems to have regressed, so I reached out to my contacts and will let you know when I hear back. Also, please let me know if it starts working again.
Just a short status update: at 2021-11-24 04:01:02, Newsblur once got a 301 redirect (can’t see the destination in the UI). Maybe somebody at Cloudflare is working on it?
Unfortunately, afterwards only 503 again 
Hopefully. I have a few feeds that are served on Cloudflare that are 503ing. I was going to wait a bit before complaining again.
As mentioned before, I can escalate within Cloudflare if you don’t get anywhere.
no improvement yet. maybe it’s a good time to accept @thedaveCA 's offer to escalate and speed things up?
We’ll it’s Monday after thanksgiving weekend so I’d give them until EOW
I reached out again today, so let’s hope that helps
A week or so ago I filed a support ticket from my paid account – they did not understand that I was describing an issue between their marketing blog and a third-party service I don’t control (NewsBlur).
This looks to be fixed!
2022-01-10 17:46:00 OK (200)
2022-01-10 17:13:00 OK (200)
2022-01-10 16:41:14 OK (200)
2022-01-10 16:08:05 OK (200)
2022-01-09 14:47:35 HTTP Error (503)
2022-01-09 14:41:47 HTTP Error (503)
2022-01-09 14:41:35 HTTP Error (503)
2022-01-09 14:41:16 HTTP Error (503)
Nice, I saw somebody tweeted at them earlier today. Wonder if that did it?
Unfortunately, it looks like the issue is back again for Cloudflare-protected blogs.
I can enter the RSS feed (https://vorek.pl/rss.xml) from my browser, but Newsblur has been producing 503 errors since mid-day yesterday.
@samuelclay, would you kindly look into this?
It’s different from the original topic. The original topic covers Cloudflares own blog, not Cloudflare-fronted 3rd party sites.
The feed for Cloudflares own blog is working perfectly in Newsblur right now.
I wonder what is triggering it? Cloudflare has a “known bots” thing that should apply to requests to feeds, and I have a few sites that have feeds that load through Cloudflare that work fine.
Individual sites might have configured challenges or other protection without exempting calls to their feed, but this would tend to hit all feed readers equally and most sites (at least, those with analytics and anyone that knows how to read 'em) would notice the loss of traffic.