This is not a major problem. If I do 10 to 15 mile trips it never happens. Then it pops out a few times in succession and may not happen again for several miles. Would changing the transmission fluid help in view of the fact it never happens when the car is cold ? The car has done 92,000 miles.
The fact that it pops out of gear is not a major issue for me as the driver. The fact that it never happens for 10 to 15 miles is something I don't understand. Is there a reason why it never happens on short journeys? Why does it not happen a mile down the road as an example?