I've installed lightroom 6, and it opens up and I can import files and develop, but then after a short period it crashes so I have to open it up again, this
happened all the time with my use last night.
I have a 2009 Mac Pro, 24GB ram. The program is installed on a SSD PCIE card.
I have tried it with and without GPU ticked, no difference in behaviour.
My setup exactly (almost, my SSD is internal), and the very same issue, crashing. Cropping, selecting several images, importing - crash, crash, crash.
Have not looked at the GPU setting yet - but I am not too hopeful...
Haven't seen a major application that unstable in years.
Just like to say all is well now, seems to be better after a nights sleep .
Imports very well, 1:1 previews take a while from a 36megapixel image.
Have you tried disabling GPU (Preferences / Performance / Use Graphic Processor) ?