hello and welcome to the forum,
In testing, I think that this is a cloudflare issue.
keep in mind that
--- R2 is beta,
--- R2 documentation states that, during the beta, the maximum number transactions per second are rate limited.
--- each provider has it own quirks, requires its own set of tweaks.
i have found that this combination of tweaked flags works around the errors.
you might need to re-tweak the settings based on your internet connection speeds.
--tps-limit=5
--s3-chunk-size=256M
and might need to tweak --s3-upload-concurrency