When I use AI0 or AI8 singly to measure a voltage, they are both OK. But when I use them simultaneously, the accuracy is bad. I wonder if only me that experience this.
Did you accidentally set terminal configuration to "differential"? Because AI0/AI8 is positive/negative input pair for differential measurement, same goes for AI1/AI9, AI2/AI10 and so on.
You could use other AI inputs for measurement or change the configuration accordingly.