I got the same error, and after a lot of trial and error i figured out it happens when strapi is nested within an existing Node project that also uses babel/webpack (in my case a Next.js project).
nextjs-project/strapi
❯ npm run build
> strapi@0.1.0 build
> strapi build
Building your admin UI with development configuration ...
✖ Webpack
Compiled with some errors in 8.49s
Error: ./.cache/plugins/strapi-plugin-content-manager/admin/src/components/RepeatableComponent/Banner.js 2:87
...
nextjs-project/strapi
❯ cd ..
nextjs-project
❯ mv strapi ../
nextjs-project
❯ cd ../strapi
Projects/badsyntax/strapi
❯ npm run build
> strapi@0.1.0 build
> strapi build
Building your admin UI with development configuration ...
✔ Webpack
Compiled successfully in 11.56s
@DMehaffy can you try replicate this issue by bootstrapping a next.js project then bootstrapping a strapi project nested within the nextjs project?