Docker file, symlink disappears mid build - bash

Question

I have the following docker file (at the bottom). I am using another image to grab a precompiled library (utilities) and copying it into the route of a new image. I then need to symlink that directory into my node_modules directory. This works fine, I have 3 places where I prove the issue.
Check for the existence of the original root directory /utilities. This works, I can see the files
Then I create the symlink: ln -sf ...
I think check to see the contents at the location of the symlink. This works, I can see the files.
I go on to create the rest of the image
At the end I again list out the files, and now I get
ls: /usr/src/app/node_modules/#boiler/utilities: No such file or directory
It's like the symlink doesn't persist. If I run the container with shell: docker run -it --entrypoint=sh backend:latest and create the symlink it works.
Any thoughts as to where my symlink is going?
FROM utilities-setup:latest as build
FROM node:8.5.0-alpine
COPY --from=build /utilities /utilities
RUN ls -l /utilities <-- 1. THIS WORKS, FILES EXIST
#setup directories
RUN mkdir -p /usr/src/app/node_modules/#boiler/
WORKDIR /usr/src/app
#create symlink to the utilities module into the boiler module
RUN ln -sf /utilities /usr/src/app/node_modules/#boiler/
RUN ls /usr/src/app/node_modules/#boiler/utilities <-- 2. THIS WORKS, FILES EXIST
#copy the content of the backend to the current direcotry
COPY . .
RUN yarn install
RUN ls /usr/src/app/node_modules/#boiler/utilities <-- 3. THIS FAILS, NO MODULE
RUN ["chmod", "+x", "./scripts/prod.sh"]
EXPOSE 8080
ENTRYPOINT ["/usr/src/app/scripts/prod.sh"]

Answer 1

[see comment] I clocked the problem.
What was happening was the yarn install was recreating the node_modules directory, so you have to create the symlink after all other modules are installed. Makes sense I suppose, but I thought it would just write to the directory if it already existed