Saved credentials problem and WPS eventually

[maxdd]

Basic Infos

Hardware

Hardware: Amica NodeMCU ESP-12

Description

Sometimes the modules doesn't connect.
A reset or a power off/on is requested.

Sketch

#include <Arduino.h>

void setup() {
     WiFi.mode(WIFI_STA);
  WiFi.begin(WiFi.SSID().c_str(),WiFi.psk().c_str()); // reading data from EPROM, last saved credentials
  while (WiFi.status() != WL_CONNECTED) {
    delay(1500);
    Serial.print(".");
  }

  wl_status_t status = WiFi.status();
  if(status == WL_CONNECTED) {
    Serial.printf("\nConnected successfull to SSID '%s'\n", WiFi.SSID().c_str());
  } else {
    Serial.printf("\nCould not connect to WiFi. state='%d'", status); 
    Serial.println("Please press WPS button on your router.\n Press any key to continue...");
    while(!Serial.available()) { ; }
    if(!startWPSPBC()) {
       Serial.println("Failed to connect with WPS :-(");  
    }
  }
}

void loop() {

}

Other

lots of dots on the serial console

Using the above code to switch to WPS in case credentials are not available, i've noticed that sometimes it works (right after 1-2 secs) sometimes it doesnt (keep showing dots).
Am i missing something? Why can't he find the credentials if after a simple reset it does?