I was having an issue with my embedded H5P activities where it was was not displaying all the time (they would just show up as a white box or some of the contents within the box would not appear) -- I would have to resize my browser or refresh the page to get the activity to appear. I wasn't sure if that was the issue you were having. To solve that issue, H5P said to remove the script tag from the embed code:
<iframe src="https://h5p.org/h5p/embed/24545" width="800" height="528" frameborder="0" allowfullscreen="allowfullscreen"></iframe><script src="https://h5p.org/sites/all/modules/h5p/library/js/h5p-resizer.js" charset="UTF-8"></script>