Hello,
I don’t know if this is your problem, but node 9.00 is the newest stuff. Maybe this cause problems.
I learned from this post --prod build not work, @ionic/app-scripts 3.0.0 broken that I would be a good idea to have the possiblity changing npm (node) version by nvm.
If https://ionicframework.com/docs/cli/ is “actual”?, then node 6 LTS should used.
Best regards, anna-liebt.