This investigation task has been put on selves since awhile, I've un-dusted it last few days.
Putting a oscilloscope on the IR Receiver , I saw some spikes to LOW, even without IR activities, especially on RESET.
Adding PullUp didn't help. Looking the specs of IR838 or VS838, the sensor is supposed to be working as low a 2.5V.
So, I've decide to add a diode and 100uF cap to separate it from the ESP VCC.
Bingo ! No more random/inconstant spikes !
ESP is rely a VCC Power gourmant !!!