Cloudflare's default settings are very hostile to RSS feeds in general. They block these as part of bot blocking. Which of course is silly because these are intended to be accessed by bots. Even Cloudflare's blog RSS feed is affected by this.
Specifically, there's a ticket in progress to improve how bot mitigation handles requests for certain types of static content (including RSS feeds).
Of course there are ways to bypass the cache with bogus URL parameters that make this difficult and some customers that are concerned with scraping even if that content is "static".