I created a custom recipe that uses "view_id": "spans" and the TXT loader. I have also set "auto_count_stream": True so I can see the percentage while going through the set. But the percentage is always not correct. It even does not reach 100% when there are no tasks anymore.
Then this might help explain the behavior. If you switch to v1.12 you should see an improvement, although we have dropped support for auto_count_stream. If you stumble apon another edge case though; we're all ears!