This is a recently problem for me (August 2016). I've been noticing that in all of my Publish Services folders, whether a Published Smart Folder or a regular Published Folder, a few times a week when I go to check to see if any new images need to be updated, I notice there is no listing of new images or updated images or images to be deleted or images that have been published. Every image in that folder simply appears it's the first time it is set to be published. In other words, the Publish button is there, but it appears that nothing has been previously published. Even though it has. Possibly as recently as the day before.
I should add that these published folders are simply set to output to a corresponding folder on my local hard drive, not to a service like Facebook or Flickr. Just a local hard drive export.
When I click the Publish button, LR thinks about it for a minute and I see the Updating Published Collections status bar in the upper left. After a few seconds, that "completes" but nothing in that folder collection appears to have changed as far as LR is concerned. There is still no indication that anything has been published or not, and the Publish button remains, highlighted as if nothing has happened.
Also, if I either manually drag an image to a non-smart published folder or add attributes to a new photo that would cause it to show up in a smart published folder, and then select either published folder, there is nothing to indicate that a new image is in there to be published. I can scroll and find the new image, but it doesn't get flagged to be published. As far as LR is concerned, that entire folder is still waiting to be published for the first time.
Further experimentation reveals that when I click on Publish, the just-added image *is* exported into the correct folder on my local hard drive. That's great, but basically now my workaround is to go through all of my publish services folders, and click on Publish on all of them because LR is not telling me whether anything needs to be updated or not. I just have to Publish everything, like it was the first time. Although not exactly, because it's not exporting images for photos that are already in my hard drive folders, as it knows those have been exported. It just seems to be keeping it a secret from me when I'm looking at a published folder.
Anyone else having this issue?
All software up to date:
Mac OS X 10.11.6
Lightroom 6.1 [Build 1083169]
Check your Metadata options and see if you have the "Remove Person data" option checked for the Hard Drive Publish service?
Toggle this option and see if it makes a difference.
There was a bug reported for an earlier version of LR6/CC2015 saying that if the "Remove Person Info" option was enabled then immediately after a Publish operation was completed the photos changed back to "Modified Photos to Re-Publish" when using the Hard Drive Publish Service.
See the thread here: