Cannot upload to R2 from pyarrow?

When trying to upload files to R2 using the pyarrow package, I get the following error:

(write_block pid=889) OSError: When uploading part for key '150gb/29e5ddef2754413caf1137621ffe2c4c_000000.parquet' in bucket 'ray-datasets': AWS Error [code 100]: Unable to parse ExceptionName: InvalidPart Message: There was a problem with the multipart upload.
(write_block pid=889) /arrow/cpp/src/arrow/io/interfaces.cc:259: Error ignored when destroying file of type N5arrow2fs12_GLOBAL__N_118ObjectOutputStreamE: IOError: When uploading part for key '150gb/29e5ddef2754413caf1137621ffe2c4c_000000.parquet' in bucket 'ray-datasets': AWS Error [code 100]: Unable to parse ExceptionName: InvalidPart Message: There was a problem with the multipart upload.

And my R2 bucket looks like this:
image

Is this a bug in Cloudflar?

Pretty sure this is a bug in Cloudflare, b/c the same code (w/ different access keys ofc) works fine when uploading to S3.