Arduino mega disconnection problem

Hi to everyone,
I have problems with the disconnection of the arduino board with the local server.

This is my setting:
-blynk local server running on raspberry (v0.41.5)
-arduino mega with ENC28J60
-v0.6.1 library

After various month of tests without this kind of problem, yesterday arduino started to disconnect from the local server…
To discard problems about the code, now I’am running this simply code:

#define BLYNK_PRINT Serial
#include <UIPEthernet.h>
#include <BlynkSimpleUIPEthernet.h>
#include <TimeLib.h>
char auth[] = "................";
IPAddress server_ip (192, 168, 0, 10);
void conta();
BlynkTimer timer;

byte arduino_mac[] = { 0xDE, 0xED, 0xBA, 0xFE, 0xFE, 0xED };
IPAddress arduino_ip ( 192,   168,   0,  11);
IPAddress dns_ip     (  8,   8,   8,   8);
IPAddress gateway_ip ( 192,   168,   0,   1);
IPAddress subnet_mask(255, 255, 255,   0);

void conta(){
  Blynk.virtualWrite(V1, millis());
  Serial.println(millis());
}

void setup() {
Serial.begin(9600);
Blynk.begin(auth, server_ip, 8080, arduino_ip, dns_ip, gateway_ip, subnet_mask, arduino_mac);
timer.setInterval(3000L, conta);
}

void loop() {
  Blynk.run();
  timer.run();
  }

But the problem remains.
If I reset arduino, it connects correctly to the server with these messages:

[0] Using static IP
[1052] IP:192.168.0.11
[1053] 
    ___  __          __
   / _ )/ /_ _____  / /__
  / _  / / // / _ \/  '_/
 /____/_/\_, /_//_/_/\_\
        /___/ v0.6.1 on Arduino Mega

[1171] Connecting to 192.168.0.10
[2736] Ready (ping: 33ms).

After few time appear the error:

[340286] Connecting to 192.168.0.10
344550
344870
[345253] Ready (ping: 703ms).
347870
350870
353870
356870
359870
362870
[365266] Heartbeat timeout
365870
[367270] Connecting to 192.168.0.10
392283
[392283] Connecting to 192.168.0.10

Sometimes it reconnect to the server and sometimes not…

Sounds like a problem with your Ethernet adapter, or possibly your router that is causing the loss of connection, thus the heartbeat error from Blynk.

So… I can try to connect the arduino board with the esp8266 module and see if the problem remain…
Could be broken the ENC28J60?
About the router… I don’t know what test could I do…