That 0Ω resistor probably fulfills a compensating role for something that after months of careful design was determined to require all the effects (that being parasitics, or nothing) of a 0Ω resistor.
That's the thing about building good shunt resistor monitoring:
You don't only need good understanding about how the circuits work on paper (which you, in all honest brutality, you really don't have yet), you also need the experience to know about the way simple components behave differently than their simple theoretical models.
You're at no point where you understand the parasitics of resistors and PCB traces. Hence, to you this 0Ω resistor isn't explicable.
To us, we don't know why it's a 0Ω resistor in that place (we can speculate, but that'd be mostly idle speculation), but we could spend a lot of time designing our own PCB that contains similar compensation/adjustment elements.
I'm very sorry to tell you this, but the comments to all your power metering questions have been so far:
This project is both too technologically involved and to dangerous for your current state of understanding.
Using an IC that you don't understand and that doesn't even come with documentation that you can read makes it even less sensible to try and do this.
Simply pick a different project. You've demonstratably (your own questions!) haven't made any significant progress at understanding the problems at hand. You need to start somewhere simpler, less hazardous. Thank you for understanding, and I hope you don't hurt yourself during your experiments with grid power.