@Deva_Rishi Sorry for late reply, Christmas time is a rush! 
Here are parameters I use to get first ESP-12F working properly.
Following your advice, I also tried with 4MB flash size. I also tried with and without erasing the full sketch. Sadly, no
I'm going to purchase a bunch from Estardyn to give them a try and I messaged the first vendor (Diymore PCB Store).
That's quite frustrating, i'm pretty sure there is a simple trick to make it work properly! 