Did they look through the start/stop parameters in the engine ECU?
There's several pages of detailed data, listing the last reason for the engine failing to stop/ failing to start/ having to restart early due to a fault/ etc, plus individual counters for any possible S/S issue (low battery, seatbelt not plugged in, A/C needing to operate, neutral position sensor, clutch/brake switch, not enough brake servo vacuum, etc).
In the event of an intermittant fault, we would print-out all the data (including the counters) and compare the data the next time the customer reported the problem- which makes identifying the cause quicker and easier.
Unfortunately not all Techs are clued-up on S/S, your best bet is to get the DET involved in your case.