Rclone fails to switch to multi-part uploads when a file is too large

If you don't want slow to start you need --s3-disable-checksum

Hmm, things to try

Try setting --s3-upload-cutoff 1T (very large) so that you only upload files with single part uploads - does that help?

Also try --s3-concurrency 2

Related threads

I suspect this is caused by some new rate limit at cloudflare - remember R2 is a relatively new service and we've seen quite a few changes in how it works over its brief life.