Theme config install settings.yml file breaks Bootstrap sub-theme

I'm having trouble with a LESS sub-theme, which appears to be related to CDN Provider configuration (but not like 💬 custom style.css not loading Closed: works as designed ).

Steps to reproduce:

1. checked out bootstrap Drupal theme 8.x-3.x-dev
2. copied less starterkit sub-theme to mytheme in sites/default/themes/mytheme and changed all the STARTERKIT references, including in mytheme.libraries.yml
3. checked out bootstrap source files in ./mytheme/bootstrap
4. compiled lessc ./mytheme/less/style.less ./mytheme/css/style.css
5. drush cr
6. enabled mytheme
7. visit homepage and see no styling ... no mytheme css or js assets
8. enable CDN (jsdeliver) in mytheme settings ... bam! bootstrap assets show up, from CDN, but of course not from local mytheme assets...

So I did some php debugging and came across the alter that runs if a provider is found with assets, where no alteration of library info should happen in the case where no CDN provider is selected/configured. Still can't quite understand how the sub-theme's libraries / assets aren't being loaded... I'll keep debugging, but in the meantime; can you reproduce this, Mark?