that turning on the viscosity after obtaining the inviscid steady state shock solution, doesn’t affect our conclusions since exactly the same result would be obtained if the viscosity is turned on initially. However, since turning on $\alpha$ makes the numerical code slow, it would have taken much longer time to search the parameters for which the disc admits shock solution. The role of viscosity is to remove angular momentum outwards, and consequently it perturbs the shock front, and may render the stationary shock unstable. In Fig. 2a, we show the time evolution of the shock location for inviscid accretion flow. The shock location is measured at the disc equatorial plane. Here, we use input parameters as $r_{\rm inj} = 50.4$, $v_{\rm inj} = - 0.06436$, $a_{\rm inj} = 0.06328$, and ${\lambda}_{\rm inj} = 1.63$ respectively. For $\alpha = 0.005$, we find stable shock at around $17r_g$ depicted in Fig. 2b. When viscosity is increased further and reached its critical limit, namely $\alpha = 0.011$, shock front starts oscillating and the oscillation sustains forever, provided the injected flow variables remain unaltered. This feature is shown in Fig. 2c. For further increase of viscosity, the oscillation becomes irregular and for even higher 