Possible bug with online IDE

I'd been having some trouble getting millis to work in a particular project's code, so after a bit of troubleshooting I ran this simple code:

void setup() 
{
  Serial.begin(9600);  
}

void loop() 
{
  Serial.println(millis());
}

I realised that the timer was jumping up by 4-6 seconds after a few returns of 0 and 1, before continuing to count normally.

E.g.

0 0 0 0 0 0 0 0 1 1 1 1 1 1 4546 4550 4554 4558 etc...

I have tried the same code and board on my offline IDE with no issue (i.e. normal counting). I also tried it on a different computer with the same results for both online and offline IDEs respectively.

I'm using Firefox on Ubuntu with a Nano copy (ATMega328P (old bootloader)).

Because it is WEB based internet speeds can come into play.

An optimised connection is always worth the effort.
Browser add-ons are best avoided.
At the user end it is also best to EXCLUDE the bridge/agent from any additional security.
Ethernet is preferable over Wi-Fi.

Those seemingly minor things can all help get better serial readings.

Better still would be to use a local serial monitor as you found with the desktop IDE.
There are other serial stand alone programs capable of much more than the desktop IDE’s built in monitor.

Bob.

Ok. Thanks for taking the time to reply.