The sampling rate is always 100k samples/sec.
I installed a 1uF ceramic capacitor, although it was a bit too large. I think the current waveform is different with and without the capacitor.
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.
Since the bypass capacitor was not mounted on the Flash breakout board, I mounted 1uF without much thought. I never thought it would affect the operation of Flash in such a way!