Since your design has no 0V reference which by definition we call the ground symbol, Falstad has chosen a different reference when the switch to the right is closed.
On a floating circuit the currents are not affected by a single placement of the ground symbol, it only changes your relative voltages.
In my simulation I used >Options> other options< to change the sample time to around 500us with the simulation slider speed to “mid scale” to get closer to a realtime display of 1 second per second as you are using longish time constants. As always all passive parts are ideal and the traces have no inductance, so I add these ESR,DCR,ESL’s for RF work to closer model the real physics.
I also created by inserting a ground symbol on the Cap-V so that Falstad Sim knows to use this for all “absolute” voltage measurements. You can put it anywhere you want as long as if you use more than 1, you are consistent. Parallel Voltages and caps cause infinite circulating currents, so in real physics, there must be some ESR. (mOhm)
Differential V measurements are possible using the right mouse Labels and stuff> Scope Probe and place the + point 1st then drag to any -ve point. Then you can choose V, Vrms, Vpp, Vmax,Vmin, etc. Add line traces to make it less interfere with the components to look good.