WebStorm local history showing up as completely blank

I tried showing local history with VCS->Local History->Show History.  This has always worked for me before but today it just came up with a blank window (see pic).

I did some Stack Overflow research and they suggested invalidating caches.  I did that and only realised too late that this also clear local history.  So I created a new file and did some editing.  The result is still the same.  I am running WS 2019.2.4 on MacOS 10.14.5.  The only two plugins I have downloaded are Material Theme UI and Rainbow Brackets.  I tried restarting WebStorm but the result is the same.  I tried putting a label, and it allowed me to enter text in a dialog, but the result was the same.

Any help appreciated.  As said, I've used Local History before on other machines in other contexts with no problem.