Files missing when connecting iPad to Windows 10
Install iTunes on your PC and connect your iPad. When iTunes launches and sees the iPad, click on the iPad icon at the top of the window to the right of the "music, movies TV Shows" icons.

Click on "Summary" on the left and you can select the options you want (apps, music, movies, pictures) to sync your media and where you want them copied to. Note that you have to have the iPad connected and selected in iTunes to make these changes.

Apple has set up IOS devices so only a limited amount of data is exposed to Windows Explorer. Why you are only seeing some of them, I am not sure, but once you set up Sync iTunes will copy all new pictures and videos to your PC.