To be fair it works absolutely fine with my S5 and the only time it’s played up with the S3 was when it was in a garage for a week - thought there may have a problem with the communicating to the car whilst it was garaged. As soon as the car was outside the app corrected itself
I had the same issue - was away on holiday for a week and after 4 days of leaving the app told me the windows and tailgate were open. The car was in my garage so wasn't bothered about whether it was actually true or not.
The Land Rover app is just as bad, it always shows the windows are open on my missus' car now.