I think what happens is you include CSS in the bundle directly. The CSS rule sees that the issuer is not html and applies style-loader additionally, which then incorrectly parses CSS as a JS module, hence the syntax error. I suggest you reread on using bootstrap with webpack. I bet if you remove CSS from vendor config it will work. In my opinion, ‘au new’ offers not the best webpack config, where you have to manually pick your vendor modules.
I’ll be able to have a look at your repo tomorrow - 11pm here