You could be disconnected if your browser is put into the background, if you switch to another tab making the Puffer tab inactive, or if the server hasn't received heartbeat messages from your client for a couple of seconds (e.g., a short network outage).
If you watch the Puffer video in full screen mode constantly without doing anything else on your computer, typically you should not be disconnected (because network outages are the relatively rare reason).
Best,
Francis