Output voltage error
Remove D7, and I think the output situation will improve.
The 1N5817 has a reverse leakage current of up to 1 mA.  That combined with resistor R17 lets the 5V rail pull the output away from its intended value.
D7 acts like a resistor and forms a voltage divider with R17.  The result is somewhere between the 5V rail and the output voltage from U2.
The 1N5817 is more for high current applications.
You'll need to find a replacement for D7 with a far lower reverse leakage current.

The ADS1115 can only tolerate 5.3V on its analog input when operating on 5.3.
You will need a diode with a low foward voltage (less than 0.3V) to really protect the ADS1115.  You will need a diode with a very small reverse leakage current to minimize the error in your protection circuit.