Docker (for Windows) does not mount volume
I found it better to try around with docker
itself, as it gives more feedback
docker run --rm -it -v C:/PROJECT_DIR/config/logstash/pipeline/:/usr/share/logstash/pipeline/ docker.elastic.co/logstash/logstash:5.6.3
From here and some googling I found out I had to reset my shared drives credentials under "Docker for Windows" -> Settings... -> Shared Drives, because I had changed my windows domain user password.
If you changed your system username or password then you need to re-apply the credentials to get the volume mount working.