CSP is blocking Cloudflare even though I rewrote the CSP header

I'm running a software called Mattermost, and whenever I proxy it through Cloudflare, I receive this error when trying to connect.

Content Security Policy: The page's settings blocked the loading of a resource at https://static.cloudflareinsights.com/beacon.min.js/v52afc6f149f6479b8c77fa569edb01181681764108816 ("script-src").

So, I used a Transform Rule to remove the CSP header. It appears to have worked, I can't see it in Firefox's inspector, but the error still appears in the console. Why might this be?
Screenshot_2023-06-21_at_9.18.50_am.png
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