I'm using the latest version of Lightroom on a CC subscription, on an iMac.
Lately I've often noticed that when I add a photo to a publish collection, such as a hard drive one, or 500px or whatever, all the photos appear in one group. The behaviour I expect is to see a "new photos to publish" group on the screen, then a "photos to republish", then a "published photos". Any idea why they would all show up together with no division between them?