Internet Connection Lost

Hi;
ever since I upgraded to the latest WP version I get very often the message that I lost internet connection while I am saving a post and that a backup is being created in the browser.

How can that be? I am on highspeed cable internet and while WP gives me this error I can access other sites with no problem, clearly indicating I have a solid internet connection.

What causes this? How can I fix this?

Thanks

Lode