Every once in a while, if I select some DNG files, or some JPG files, it does let me drag all of them, but most of time it just deselects all the rest, and refuses to let me add even that one image. I also tested this using other older files that were previously downloaded normally, and but Lightroom is deselecting the other two as well most, but not all, of the time.
I have never seen this
behavior before, so I am perplexed. Strangely, I spent hours earlier today
going through older images, and LRC let me drag one or more items to a different
collection just fine. It’s very frustrating not to be able to add all these new
files to a collection I have, as my workflow has ground to a halt.