I just installing Lightroom 6 desktop on my MacBook, and it quits after a few minutes of working in an existing catalog. I am unsure what the issue is. I have attempted to uninstall and reinstall LR several times, and I am getting the same results.
If you haven't done so already, go to the performance tab in Lightroom preferences and uncheck the GPU option.
Please make sure that Lightroom is upto date and has the latest version 6.2.1
Also please try the following steps :