I faced the same problem.
Decided to change my (duo)valve.
Its cost (120.00) encouraged me not to pursue a much more complex and expensive possibility (such as a kind of alzheimer in the a/c electronics)
If the fix works, Ok.
If not will go further.
The car is 10 years old and chances are im my favour.
In between: I don't know why but heavy traffic used to provoke the symptom. Also, keeping the termostat a bit lower tends to minimize it.
The replacement is in process.
I will post here if the issue goes on.
Jorge