pm2 start error : Script index.js had too many unstable restarts (15). Stopped. "errored"

https://lifesaver.codes/answer/too-many-unstable-restarts

Are you using nvm or n to install pm2?
I think it's due to a bad node version from the modules. Please try:

pm2 kill
rm -rf node_modules
npm i
pm2 start index.js -xn 'myapp'