I have a catalog created on a machine running Mavericks (currently 10.14.1) using the then current Lightroom Classic CC (version 7.something). I have upgraded to Lightroom Classic CC version 8.0. The catalog opens fine. I connected my disk to a machine running High Sierra (currently 10.13.6) and Lightroom Classic CC version 8.0. When I try to open the catalog on the High Sierra machine, Lightroom hangs. The splash screen appears. Some temp files come and go and come and go and come and go and come and go ... in the directory with the .lrcat file but Lightroom never gets beyond the splash screen. I force quit Lightroom. I reconnect my disk to my Mavericks machine, and Lightroom works fine. Any ideas? This is 100% repeatable with my catalog. I am pretty much dead in the water for this catalog, because my High Sierra machine is my work horse, and it cannot be upgraded as I have some apps that are dependent on High Sierra (for now). Is there any way around this? Is there a way to (mostly automatically) create a new, compatible catalog with all the information that is currently in the catalog that does not work on High Sierra? If I do that and then open the catalog on a Mavericks machine, will the catalog be broken again?