Hello there! I have a 2013 Mac Pro that had 16Gb - all 4 slots filled with 4Gb each. Working with Photos, and with the price of memory being what it is, I thought it would be worth the roughly $100 to upgrade to 32Gb. So I bought a kit, with 4 8Gb modules. After upgrading, it shows I have 24Gb, with one slot empty. Thinking maybe one module was bad, I tried moving them around - same slot shows empty, still only 24Gb. Any thoughts? Thanks for the help!