Auto Box Torque Convertor slip (sound like going over a cattle grid) between 50-60KPH very occasionally when changing up in humid weather. Lasts for about a second.

Just been to see my auto box mechanic again and he says these gearboxes do do this and he would not do anything as it can go away. If the convertor or solenoid packs up you will know and that’s the time to repair it.
Does this sound right ??