What does "GND" attach to ?
If it has a significant leakage to earth - either directly or via other instrumentation, then you have shorted-out half of your potential divider. To obtain a reliable measurement the ACS37800 and associated circuitry must be floating.
Well it seems that the negative input of the voltage sensor which was also connected to ground was connected to VAC (240v, through 1M*2 resistors) but it should have been connected to Neutral, same goes for the positive input of the sensor (was connected to neutral when it should have been 240v). And that seemed to fix the problem, but I have yet to test it at 110v.
Shouldn't IP+ be connected to the live mains lead rather than NEUT?
Nope, IP+ is part of current sensing feature of the chip. If I were to connect it to LIVE I would have shorted out the mains. But if you were talking about VINP, then you are correct.
What are the tolerances of the resistors? How are you measuring the 107 and 117? If the resistors were identical you wouldn't see that 10V difference. How pure is the wave?
The resistor has a tolerance of 5% but I don't think it's big enough to make changes of >40v. Although I should go with lower tolerances for next iteration for increased accuracy.
One of the reasons could be your expectations are incorrect. The universe is never wrong. What is the voltage rating of your resistors, how are they assembled, what flux did you use and does it need cleaning after?
Each resistor has a max working voltage of 200v, so they should be fine. But I didn't know that the flux might sometimes need to be cleaned, I'll look more into that.
Additionally, I see bad soldering in the photo.
Well.. it was my second attempt at SMD soldering.
Thanks for taking the time to help me