Debugging in WebStorm with WebPack source maps produces strange errors that don't appear in non WS-launched Chrome instance

I'm trying to debug a Node/React application using WebStorm.  The application uses Node to mount a server which serves already built React .js files.  So in order to debug the front end using the original source code I need to produce source maps.  This is the first time I've done this.  

I modified the existing scripts to produce one that will produce source maps:

package.json

"build:dev": "cross-env NODE_ENV=development webpack --config internals/webpack/webpack.dev.babel.js --color -p --progress",

webpack.dev.babeljs

// Emit a source map for easier debugging
devtool: 'inline-source-map',

Then I set up configurations in WebStorm to debug Node and React at the same time.  I get a series of errors in the WebStorm debugger console: 

These also appear in the console of the Chrome instance launched by WebStorm.

However if I go to separate Chrome instance these errors _don't_ appear in the console: the page loads fine.

WebStorm 2019.2.4, MacOS 10.14.5, Node 12.13.0.   Any help much appreciated -- I'm at a loss.