files_upload_v2 doesn't work with CarouselBlock

[sealogfish]

I am trying to upload multiple base64 files to Slack using client.files_upload_v2(). The files are uploaded successfully but I am unable to render them in a CarouselBlock. I have no issues rendering the files as ImageBlocks. Does CarouselBlock support private Slack files?

Reproducible in:

The Slack SDK version

slack-bolt==1.18.0
slack_sdk==3.35.0

Python runtime version

Python 3.10.10

(Paste the output of python --version)

OS info

ProductName: macOS
ProductVersion: 26.5.2
BuildVersion: 25F8

Steps to reproduce:

1. client.files_info() to check if the file has been uploaded by checking the mimetype and filetype. I extract and return the permalink generated.
2. Populate the CarouselBlock with the code below:

    def build_chart_carousel_blocks(self, charts) -> list[dict[str, Any]]:
        """
        Builds and returns a chart carousel block.
        """
        cards = []
        for chart in charts:
            cards.append(CardBlock(
                hero_image=ImageBlock(
                    slack_file=SlackFile(url=chart.permalink),
                    alt_text=chart.title,
                ).to_dict(),
                title=PlainTextObject(text=chart.title),
            ))

        return [CarouselBlock(elements=cards).to_dict()]

3. Send the message using the blocks parameter in client.chat_postMessage()

Expected result:

The Carousel is rendered with the successfully upload Slack file object

Actual result:

This results in a Carousel rendered as follows:

I do not encounter this issue when I render and send an ImageBlock instead. The only workaround I managed to find was adding channel and thread_ts as a parameter to files_upload_v2(). However, this will result in double images being sent (once by the file upload command, and a second time when I render the Carousel block), which is not ideal.