Current source driving capacitor in LTspice
I'm posting the answer since it is instructive to see what can happen with the default timestep when the simulation spans too big an interval.

This is the circuit in LTSpice.



A minimum time step of 50us is more than adequate to give a stable solution on 200 ms interval:



But take it to 60us with .tran 0 200m 0 60u startup and you will see the solution drifting toward the time axis:



With 100us timestep we get shape similar - but only similar - to an exponential decay of the mean value