Doesn't trigger a rebuild/refresh for changes in css

With this project, when running make serve and after changing something in the css, the changes are registered by browsersync:

[BS] File changed: src/css/index.css

But there's no rebuild and no refresh. When I change something to a template however, a rebuild and subsequent refresh are successfully triggered. Any idea what could be causing this? It should be rebuilding in both cases right?

Might be because I'm importing css, and only the changed file is passed through the pipeline (instead of the main import)? Maybe an option to reprocess all files (or all files of the same filetype) would solve this.