It is starving the boost converter of the input voltage...
depending on your load current, the (load current + quiescent current ) * 100 ohms will be dropped across the ammeters internal resistance..
and 3.6 - (the voltage across the 100 ohm resistor) is what is actually available to the boost converter to boost upto your output voltage...
If this value is too low, then the boost converter tends to go almost 100% duty cycle, which is basically the boost switch shorting the output.