[Solved] PM2: Current process list is not synchronized with saved list

I am using AWS EC2 and runing ubuntu.

I encountered a problem where pm2 showed: 'Current process list is not synchronized with the saved list. App XXX differs. Type 'pm2 save' to synchronize.

*the XXX is my app name.

In cmd, I inputted:

"sudo env PATH=$PATH:/usr/bin pm2 startup systemd -u ubuntu --hp /home/ubuntu"

then, "pm2 save" again.

"sudo reboot"

All apps in pm2 startup automatically.

Maybe "pm2 startup -u ubuntu" also works too.