This usually occurs when people seek over and over again and their connection to Wowza is too slow to respond. This feature will refuse seek attempts until the backed up content has been delivered to the client.
If a user seeks over and over again and their bandwidth is lower than the bitrate of the video then the connection will get more and more behind. This feature attempts to stop responding to the seek requests so the connection does not cause memory run-up server side.
You can control the number of seeks that occur before this feature kicks in using the following Streams/Properties in conf/[application]/Application.xml:
Setting this value to 0 will turn off the feature but could lead to memory run-up server-side.
If seeking is not the issue then it sounds like a bitrate vs bandwidth problem. You might want to try a lower bitrate and see if that fixes the issue.