I have not tried that time and temperature but with a little searching I found reports of the same thing when eggs are cooked for a long time at lower temperatures. Try this and see how it works for you:
For an extra large egg try 75 °C for 13-15 minutes). This is for a straight from the refrigerator egg. If you are live in a country that does not wash and refrigerate their eggs I would reduce the time a minute or two. A couple of experiments and you will have perfect eggs. Also, age matters with eggs. As the eggs age the whites become more fluid and it becomes increasingly difficult to get perfect results. No danger just more runny stuff to drain off. I get my eggs from a small local grocery that gets deliveries from a farm every day. I get the Jumbos so my times are a little different. The yolks are also a bit darker and have more flavor. With the Jumbos I also normally get 1-2 double yolkers per dozen.