unity gain buffer large input offset voltage
I believe you have exceeded the input common-mode range that the opamp supports.

The data-sheet does not give an explicit range for 3.3V operation but when operating from 2.7V or 5V the maximum is about 0.8V from the positive rail - this would be 2.5V in your situation.

Although the device has a rail-rail output it does not support operation close to the positive rail on the input.

You have a couple of options: substitute another pin-compatible device that does support rail-to-rail input or reconfigure the circuit with some gain, for example 1.5 times, such that the input is within the allowed range.


Datasheet