Image missing in media library

Hi Guys. Hope you can help.

When I “Add Listing” or “Add Event” and I try to upload images (I go to “Drop files to upload” on the bottom) NOT all images show up in my media library. The first picture shows up in my media library, but the other pictures never show up in the media library. Where are the other images?

Reading a post on this from 2014 or so, it stated something like you guys ONLY load the first picture into the media library and the other images are not loaded into the media library. You do this because otherwise it will slow down performance.

I am using Shortpixel plugin to compress and optimize my images. Now, if only 1 picture loads in the media library out of lets say 3, that means 2 images will NOT be compressed and optimized as they are not loaded into the media libarry. So, the question is where are these other 2 pictures? Which folders do you keep them in? I can add that folder to shortpixel and it will compress and optimize pictures from that folder. So, I basically need to know which folders are images 2 and 3 being stored in? Pic 1 is in media library folder. Which folder is images 2 and 3 going into? If I can find this folder it can be compressed by shortpixel. Thanks.

Any other solution to this problem? How are people compressing and optimizing their images if only the first one ends up in the media library for a listing. What if someone has 5 images for a listing. Image 1 goes into the media library and is optimized by Shortpixel plugin. Where do images 2 to 4 go and how can they be optimized by the plugin.

Hope I explained this well. Pls help.
Thanks again guys.