Buck-boost INPUT voltage regulation stability (MPPT)
This is a slightly unusual use of this device according to the data sheet but, I can see it operating with a little more care in component selection. See figure 9 in the data sheet for the loop compensation network applied across what is R3 in your diagram. I suggest that you do use the type II compensation scheme because of the addition of the op-amp in the feedback path.

I would also suggest that you use the run pin so that the initial starting transient is also avoided. You could use a capacitor on this pin to create a soft starting circuit.