NodeMCU keeps disconnecting
I had this same issue with an ESP8266 NodeMCU-12E using Cayenne in the past. It would drop connection for no apparent reason, but no matter what, most of the time it'd never reconnect until a reset. Here's what I did:

CAYENNE_DISCONNECTED(){
  Serial.println(F("Cayenne disconnected, rebooting..."));
  ESP.restart();
}


I've never used Blynk before, but after a quick look, this may do the same thing (untested):

if (! Blynk.connected){
  Serial.println(F("Blynk disconnected, rebooting..."));
  ESP.restart();
}


It effectively reboots the ESP unit if the connection to Blynk drops for any reason.