Apparently-valid feed showing up as "Not an RSS feed (553)

My own site’s feed seems to be failing to load as of my last post, but the W3C service says that it is valid. It does call out a couple of issues that might cause interoperability problems, but none of them appear to be new things – they’re things that NewsBlur had no trouble with in the past.

The URL that I’m testing in NewsBlur is Giles' blog, which redirects to Giles' blog.

Here’s the W3C validator results: Feed Validator Results: https://www.gilesthomas.com/feed/rss.xml

Is there any way to find out what might be causing the problem? The feed is generated by my own static site generator, so I should be able to fix it – I think that a reasonable number of people subscribe to my site over NewsBlur.

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I refreshed it and the stories came through: NewsBlur

So I wonder if you have Cloudflare AI-blocker or bot-blocker enabled? That could cause NewsBlur to fail to fetch your feed.

It’s showing up for me now too – thanks! I don’t have anything that might block it – it’s just a static file. Though I suppose my hosting provider might have blacklisted the IP – that would normally only happen if it was hammering them, though. It looks to me like it was coming up with that 553 error at 2025-08-21 06:09:27, but then worked at 2025-08-21 06:09:58. Was there any change between those times? Perhaps the IP address that the requests were coming from?