Following How to grant scope to also upload captions on YouTube , I programmed the upload of subtitle or caption files to videos on my channel:

  try:
    # If the subtitles do not exist, add them
    youtube.captions().insert(
      part="snippet",
      body=snippet,
      media_body=fp
    ).execute()
    print(f'{new_lg} inserted successfully!')
  except Exception as e:
    print(f'An error occurred:', str(e))

The code executes without error and the subtitles show on YouTube, for example this video:

but YouTube Studio does not show a subtitle file for the same video, even after 24 hours:

If I upload the same subtitle file manually on YouTube Studio, then it does show on both.

How can I ensure that the subtitle files I upload programmatically also appear on YouTube Studio?