Please add the following property to the LiveStreamPacketizer/Properties container in Application.xml.
This instructs the Wowza to log information for every HTTP chunk that's created (not just the first 10 chunks).
If you could post the logs showing chunks created for the stream with the issue that would be great.
After editing the Application.xml you will need to restart after saving for the changes to take effect.
Generally chunks vary in size when the keyframe frequency is not fixed as chunks are created on keyframes.
We recommend a keyframe be added every 1-4 seconds for live streaming.