The side panels suddenly go dark, though the actual grid and individual views show up as normal in Library and Develop modes. I've checked everything and searched online. At this point, only quitting and reopening gets the panels back, though this only temporarily. Any ideas?
It's a known bug.
As you've already established you can restart, but issue will return. Alternatively, and probably best, you can roll back to 6.7 Instructions can be found at Lightroom roll back to prior update version
Well, at least there's the consolation of the 'known bug,' and the faith that they'll fix it eventually. Thanks for replying.