grunt tasks hanging and not responding

Question

this is the first time I have this problem. I always use pretty much the same gruntfile configurations but at some point, my tasks are just hanging. more precisely they hang when triggered by grunt-contrib-watch. here's my config

watch: {
            css: {
                files: ['source/css/**/*.scss'],
                tasks: ['sass:dist','sass:styleguide_specific_styles', 'postcss', 'shell:patternlab_css'],
                options: {
                    spawn: false,
                }
            },
        styleguide_specific_styles: {
            files: ['public/styleguide/css/styleguide-specific.scss'],
            tasks: ['sass:styleguide_specific_styles','sass:dist','shell:patternlab_css'],
            options: {
                spawn: false
            }
        },
        }, //end of watch task

and my sass task

sass: {
            styleguide_specific_styles: {
                options: {
                    style: 'nested',
                    compass: 'true'
                },
                files: {
                    'public/styleguide/css/styleguide-specific.css': 'public/styleguide/css/styleguide-specific.scss'
                }
            },
            dist: {
                options: {
                    style: 'nested',
                    compass: 'true'
                },
                files: {
                    'source/css/styleguide.css': 'source/css/styleguide.scss'
                }
            }
        }, //end of sass

When i edit and save an .scss file, i get stuck with this:

But if i stop grunt and just type grunt sass the compilation is successful.

I've tried removing compass, freshly reinstalling all dependencies copying the project elsewhere, updating grunt-contrib-sass , updating the sass gem, changing file permissions, updating nodejs but nothing seems to work. I'm on windows using this gruntfile config on a patternlab-php project.

The same configuration works on dozens of other projects, but not here. And this is not the only task giving me this problem, all the others do the same.