What could cause a JSPM bundled module to seek to load from jspm_packages? - systemjs

Question

On a bundled production build I see a network request for: systemjs-plugin-babel#0.0.21.json from cache... on the same instance where it's unable to load fully all the way through to my app.
It fails to load anything being routed from http://thehost/myapp/jspm_packages/npm
My understanding is that in a bundled JSPM module it shouldn't ever load from this kind of route since everything is bundled into the build.js file.
I currently bundle my application with the following gulp task:
gulp.task('jspm-bundle', plugins.shell.task([
'node node_modules/jspm/jspm.js bundle myapp/index.jsx' +
' + myapp/things/**/*.jsx + myapp/otherthings/**/*.jsx' +
' + systemjs-plugin-babel + babel-preset-stage-0 + transform-react-jsx' +
' + transform-decorators-legacy' +
' --minify --skip-source-maps'
])
I'm not sure where to start... could someone tell me a few of the reasons why a bundled app would even attempt to make this kind of request to the browser?
Update 1:
At one point we saw a promise rejection that seemed related as well for this singular client:
Unhandled promise rejection Error: Syntax Error
Instantiating http://myhost/myapp/jspm_packages/npm/systemjs-plugin-babel#0.0.21.json
Loading http://myhost/myapp/jspm_packages/npm/systemjs-plugin-babel#0.0.21.json
Unable to fetch package configuration file http://myhost/myapp/jspm_packages/npm/systemjs-plugin-babel#0.0.21.json
Resolving plugin-babel to http://myhost/myapp/app/index.jsx
Resolving myapp/index.jsx
Loading myapp/index.jsx
Update 2:
My FULL SystemJS config: https://pastebin.com/aJFPqNGn
Update 3 (last update?):
I can recreate the issue in production if I explicitly import from 'npm:systemjs-plugin-babel' but I can't explain why this import would occur in production at the client's installation yet. The syntax error occurs because the request for the non-existent file returns the login html and the syntax error occurs on the first '<' in the html