Have you tried the Save email attachments to Dropbox template? I believe that is what you are using but I want to make sure. As you can see by my screenshot of this template below, the File name and File content for the Dropbox step are dynamically created. Have you tired using the dynamic naming with the Attachment name parameter? Your issue may be the hard-coded test.csv file name.
Outside of that, as @v-alzhan-msft requested, the full run history of the Flow would provide some insight as well.
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