i have same problem,
if you connectinc using DHCP , connection drops after 60 minuts
its easily fix problem
You need to use Ethernet.maintain() every 15-30 minuts
unsigned long previousMillis = 0;
int interval = 900000;
void loop()
{
unsigned long currentMillis = millis();
if(currentMillis - previousMillis > interval)
{
previousMillis = currentMillis;
Ethernet.maintain();
delay(100);
}
}