Statfile writing seeks to the length of the file between writing new data. The cached length of the file isn't updated when written to when the file length increases so it keeps going to the original length.
Launch a development project on Android
In console: stat startfile
In console: stat stopfile
look at ue4stats file (look at log for message about file location and name) and make sure the length increased
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-35558 in the post.