Missing photos in Develop. Can’t locate (!)

"Photos are not staying in Lightroom Classic after loading."

Can you explain in more detail? Do you mean they are nowhere in the Catalog Library? Where are you looking in the LrC UI, which Panel? What folder are your photos files downloading to when you Import (the Destination)?

"Also, someone changed metadata on a photo."

That would have to be you, by using another App with the files, or some software in your system that is accessing the files. What "metadata" is changing? How do you know it is changing?

"I tried an edit, selected a photo in Library, when going the Develop module the photo changed."

Changed how? Changed color? Changed image subject?

Are you aware that after importing (a raw image file), your library may show the Camera embedded preview in the Library, and when you go to the Develop module LrC is using the raw image data to create the preview you now see (possibly different to the Camera!)?