I am specifying captions as suggested in the docs: In a markdown cell I write down the caption, and edit its medata to show

{
  "ipub": {
    "caption": "fig:mylabel"
  }
}

Then I specify the metadata of the figure cell as

{
  "ipub": {
    "figure": {
      "width": 0.6,
      "widefigure": false,
      "caption": "",
      "label": "fig:mylabel",
      "placement": "H",
      "height": 0.4
    }
  }
}

I then convert the nb to html through:

nbpublish -lb -f html_ipypublish_main mynb.ipynb --pdf-debug --clear-files

however the caption appears above and below the figure once rendered to html. Any way to solve this?
edit: interestingly, this only seems to happen with figures and not with tables.
edit2: specifying the caption only in the metadata of the figure cell still shows caption both above and below the cell.