OK, I seemed to have narrowed down the problem..
The histograms don't show only with Canon G7X files that have been converted to DNG.. For native G7X .CR2 files, the histograms show. However, my other cams that have either been converted to DNG, or native DNG, show the histograms.
The Base Characteristics show "Canon PowerShot G7 X Generic", but no matter what is chosen there, the histograms still don't show.
I think I found a bug..??