Thanks for the reply. I just had the issue happen again and remembered that there was a reply here.
I'm on Mac OS X 10.13.3 (Build 17D102)
Adobe Lightroom Classic  aka 7.2
I haven't tried GPU acceleration so I'll go deactivate that now.
Issue persists with GPU acceleration off.
Which developments do you have checked and are trying to copy?
Does it crash when you try to copy or when you try to paste?
Can you post a screen-capture of the copy selection?