Thanks for the advice. After adding the 1uF capacitor, I can repeat the same waveform as your measurement.
Regarding the current after the 3rd read, if capacitor added it shows the same value (~5uA) as per delay period. Without the capacitor, the current is always ~200uA unless I suspend the loop. I am unable to explain this. I can only say current measurement under RTOS environment is tricky and is different from traditional measurement.