Op-amp input signal problem, mismatched
You are driving a signal down the transmission line that goes below 0 volts. 0 volts is also the most negative supply voltage to your op-amp therefore, you are likely to be causing the op-amp to exceed it's common-mode input range (-0.1 volts to Vcc+0.1 volts).
Of course, it's only a model so no real damage.
You are also pretty close to the limits from what you can expect with the model for your transmission line. It appears you are specifying &quot;per metre&quot; values for R, L, G and C and, at 50 MHz, free-space has a wavelength of 6 metres but probably only about 4 metres in a cable therefore, you are likely to be asking too much from the t-line model.