Hello
I can help you with this problem.
I am a Otis Employees and have been working in the trade for 26 years.

The problem as you said has not happened under usage,
It actually happens upon relevling.

It can happen when hot or if sensor is set too high but you have stated those have been accounted for.

Its in the valve but not what someone else may have already said it was.

Its seapage in the down speed and down leveling seals.

Have a seal replacement kit installed for the pair of down vales and your problem will stop.

If you can tell me the name and numbers on your valve, I can tell you the seal kit you need.
Most likely a Maxton UC4.

Let me know.

Rick