ESP8266 Community Forum 

... weeks. Two things have significantly reduced the issue. A: I only call WiFi.begin() to reconnect. Everything else like hostname, Wifi.mode() or WiFi.persistent() are only set once in the setup. The values remain even with WiFi.disconnect(true). B: Probably the most important thing. Deactivating ...

... delay( 1 ); // Disable the WiFi persistence. The ESP8266 will not load and save WiFi settings unnecessarily in the flash memory. WiFi.persistent( false ); Serial.println("Start WiFi"); // Bring up the WiFi connection WiFi.mode( WIFI_STA ); WiFi.config( ip, dns, gateway, ...

... the examples): void setup() { Serial.begin(115200); delay(200); Serial.println(); Serial.print("Connecting to "); Serial.println(ssid); WiFi.persistent(false); WiFi.mode(WIFI_STA); WiFi.begin(ssid, pass); while (WiFi.status() != WL_CONNECTED) { delay(1000); Serial.print("."); ...

... memory. " and " If your project is going to be restarting frequently (like going in and out of deep sleep often) I'd definitely use WiFi.persistent(false) to avoid wear on the flash. " Most of my projects use deep sleep cycling to save battery power. The Arduino Core documentation ...