I am a Mac user. I have the newest paid version of Lightroom CC (2015.10) and have the Lightroom Mobile and CC apps downloaded to my iPad. My "Sync with Lightroom Mobile" setting is turned on in Lightroom desktop but the button to sync a collection is not visible. I have tried logging out of all apps and back in, and even deleting and redownloading apps all to no avail. What is the issue? Screenshot below
The issue is that you cannot synchronize smart collections. You must create static collections in order to synchronize with Lightroom Mobile.
Thank you — this was it!