Rendering stops by itself!
If your rendering seems to randomly stop by itself, or before the specified rendering limit is reached, make sure that some other rendering limit is not stopping it. For example if you are using a pass limit to determine when the rendering should be stopped, make sure that noise limit, or time limit is not enabled. Corona will stop rendering when whichever of the rendering limits is reached.
To learn more about rendering limits, see: How to set limit for rendering?