I use XQuartz 99.9% of the time I'm on my Mac. When I lock my screen (using Lock Screen in the apple menu) -- or the screen saver kicks in -- and the screen remains locked/darkened for more than a few minutes -- not sure what the minimum amount of time is for this -- the screen background is often black when I unlock the screen or wake up the display. I am still able to see and use everything on the desktop -- mac icons, mac apps, X window apps, etc. -- but the screen background is black -- really hard on the eyes! If I exit XQuartz, my screen returns to normal but this is not a solution since I then lose all my X applications. If I lock the screen and immediately unlock it, I don't see the problem.
I'm running macOS High Sierra (10.13.6) and XQuartz 2.7.11. I have had my Mac (it's a work mac) since May, 2017. The Mac came with Sierra and I installed High Sierra early last fall but did not start having this problem until January. It mysteriously went away for a few months but has now returned.
Any ideas or suggestions? I'd be happy with a reasonable workaround that doesn't involve killing XQuartz.