My bus arrived earlier / later than predicted in the app
Occasionally, buses will arrive earlier / later than expected, this can be down to unforeseen circumstances on the road such as an accident that has just occurred which could increase the wait time e.g. your countdown will have shown 6 minutes then 5 minutes but then show 9 minutes.
In most cases the data is wrong because the GPS tracker on the bus is not working correctly meaning there can be a delay in it transmitting, so the data you are receiving is already a few minutes old making it seem as though the bus has arrived earlier than expected. The tracker can also send false data when malfunctioning and even fail completely / restart which may show the bus disappearing / reappearing from the app.
If you have experienced this issue you can report it to TfL directly by clicking here. You will need to provide the date/time, route and location of the issue along with your contact information.