Issue with generation of original code.

I am working on seeing how one could reconstruct the code from my frontend UI that is built in react, it uses webpack for build creationg and i have a bundle and it's mapping. For some reason i see the source lines with stripped, with further inspection i found that those reffer to content which wasn't regenerated.

Any reason to why it would happen as there are no additional steps that i have taken during my build creation.