I am using OS X 10.11 - upgraded 2-3 weeks ago. Current LR version CC 2015.2.1 - upgraded 14 days ago. Prior version number of LR CC 2015 I do not know, but it was the most recent version based on what was pushed out to me from creative cloud. that was download 101 days ago, probably soon after adobe released it.
My upgrade process was simple, so I thought. Went to the Creative cloud drop down menu and downloaded the latest version ( upgrade) of LR. Days later I noticed some missing images . found "find all missing photos" from Library drop down menu. Subsequently noticed several more images were still missing. Just spent days going through every image file on my computer with no luck in finding my images, but did find the original RAW image. Called /chatted with tech support. They added an old library ( 2014)?, then told me I no longer had missing images. But I still do have several missing images.