I also had the same error for quite a while in recent past, and below is what fixed it for me.
I just declared in service that i use what is given below :
Description= The node service description
Please note "After=network.target". I spent many days looking for the fixes on nginx side, while my problem was just that. To be very sure just stop running the node service you have and launch the ExecStart command directly and try to just reproduce the bug. If it does not show up, it clearly means that your service has all the problems. This is how I found my answer.