copying to an empty folder doesn’t work right away, you need to go into that folder and execute
sudo npm install. I have a fresh raspberry pi with pimatic and everything installs fine.
edit: Just tried it on my main pimatic installation and a everything just works fine. What i did:
cd /home/pi/pimatic-app sudo npm i DheerajKhajuria/pimatic-mysensors#ethernet sudo service pimatic restart
and done. So probably somethings is wrong with your installation somewhere.