excessive gain at low frequencies
I have put the s parameter file in Ad Lab Plus and played with series and shunt feedback. There is no way to stabilize the transistor at lower frequencies because the gain is so high. Unless you can use resistors in your design, such as in shunt with the input and output, you are stuck with figuring out an input and output network that stays in the center and bottom right end of the smith chart.
Is this a school project where you cannot change anything or a project where you can change the transistor bias point or even use another transistor?
The gain going up so much at low frequencies is a very poor situation with microwave transistors which is why they are made with low gains at low frequencies.