[rocek]

Thanks for looking into it; sounds like it is device specific.  I'm probably not going for the reset (I use the Pixelbook for too many things for it to be worth the hassle), and perhaps a future OS update will fix it.  Meanwhile, I can use my chrome plugin to lock the screen on when needed.  Thanks again for looking into it!

Just a follow-up; I don't know whether it was one of the operating system updates or a sheets update, but the problem has gone way; the screen stays on now.