I'm using a Mac Pro Retina. When using Lightroom CC recently, I was able to use the 'Sort with Custom Order' option (the option under 'View' was 'Sort > Custom order was available) The option was available, too, at the bottom of the page. I tried to Sort 'Custom Order' again, but the options were greyed out.
No matter which folder I tried, I couldn't get it to work. Tried to click out from Library 'Show Photos in Sub folders,' but to no avail. Can you please let me know what I'm obviously doing wrong. Thanks.