Why are just some of the images/videos of my collection visible in OpenSea and the rest don't appear?

In most of the cases where you see some of your files and the rest don't appear in OpenSea, it's related to the cache from OpenSea platform.

Please, do the following:

1. Go to opensea.io
2. Open one of the NFTs that aren't visible.
3. Click on the three dots on the top right of the screen.
4. Click the refresh metadata.
5. Reload the page.