Preview data is different from the actual ingestion and therefore doesn’t represent the final data ingested. Previewing data is just a way to see what the data will look like. In order to get the data back in a reasonable time, the preview data might not follow the exact parameters that you specified.
You might encounter situations in which there are no records to preview:
There is no data to preview for the data criteria specified
The API takes too long and times out and Treasure Data can’t fetch the preview data