Resource stopwords not found

When locally running constrainfy-core (with Redis, and QPM as backend) an error is thrown as soon as a constraint parameter is edited:

Resource stopwords not found.
Please use the NLTK Downloader to obtain the resource:

 >>> import nltk
 >>> nltk.download('stopwords')

It looks like there are additional dependencies not installed via pip install --no-cache-dir -r requirements.txt.