Oscilloscope range affecting voltage reading
Range      Reading
200 mV ==&gt; 1.76 V
500 mV ==&gt; 4.39 V


I can't see that second reading on your trace.



Figure 1. On the 500 mV/div range you are reading > 3 x 500 mV and the (b) reading is 1.76 V, the same as your 200 mV/div range reading.

I don't think the scope is at fault.