I'm using a 3.5 GHZ IMAC with Sierra IOS installed on it with Lightroom 6.7. I have 32 Gig of RAM and and 998 Gig Solid State Drive with a ton of memory left over. I store my photos on a 4 TByte G Drive that is connected to computer with Apple thunderbolt communication. I can use all my other photo programs and go onto the Internet for hours and never have any problems with the computer. I'm working on and exporting on photos from a Nikon D810 so the files are large.
Intermittently when I quit Lightroom 6.7 my computer goes to black screen and then a error message comes up stating an error has occured and computer will restart. After restart I can open a error report that deals with error with LIghtroom and Kernal. Did not get screen capture of that yet. Before I was running on El Captain IOS and LIghtroom 6 and I had multiple crashes in a row when trying to export .dng files and convert to .jpg. So I decided to update the IOS to Sierra and then I updated Lightroom to 6.7 which has improved things but I still had a crash when closing lightroom after working on a large file. I have increased the cache size to 10 Gig but that did not help. Has anyone had this problem? JD
Try and turn off the graphics processor from the Lightroom preferences and check if that makes any difference.
Go to Lightroom Preferences from the Edit menu
Click on Performance tab
Uncheck the Graphics Processor