We have found that there is a bit of an overlap between the launch button and the down shift paddle graphics (see screenshot). If you tap on this area (marked in red) it may cause the launch to not register. This will be fixed in our next update which, unfortunately due to the holidays, won’t be able to get approved in time, so it will have to wait until January.
For now, if you tap the launch button in the area shown here in green, you will be able to launch your car as normal.
We apologize for any inconvenience and appreciate everyone’s help in investigating this issue and for your patience.