Gallery Block doesn’t Allow New Images

Problem:
clicking “Media Library” at the bottom of the gallery block to add a new image replaces the entire gallery.

If I click upload a bunch of images to add to a gallery block and then go to the gallery block to edit and add to it via the Media Library link, that brings up a page to ‘reorder gallery’ – ONLY the new media is shown. Clicking ‘Update Gallery’ replaces the ENTIRE gallery with just the one image.

Obviously, it’s not supposed to work like this. There is no work around other than just using the ‘upload’ button but that’s dumb. The other button is useless.