I'm not sure what changed to solve my erratic app connectivity as there were too many factors to pinpoint the exact one - change of phone, connecting the car to my home wi-fi and a software update(s) to name just three.lordrobs agreed, he looks out the window which is only the behaviour I want to assure, sure parents would like that too, corsa-e owner I discussed with said they used that - so you wouldn't knowingly buy a charger/car combination that precluded it with poor mobile coverage ... akin to having car play in an older ice say, ability to pre-condition en route to minimize stopping time also 'useful'.
Whatever the case if the car is locked and plugged in it now seems to connect every time in the app which is why I use the pre-conditioning on an ad-hoc basis. The cost I reference kind of tongue in cheek (although it is a factor) but the added flexibility in being able to leave earlier or later is the key benefit of not pre-scheduling in the car, which required no coverage whatsoever.
Honestly though, the heat up time is so minimal that if I couldn't do it I wouldn't be that worried. The instant warm air being by far the bigger factor than any pre-conditioning ability.