We can’t troubleshoot in the forums since we need to run several tests on your Engine configuration and look at your CPU usage more closely, so please send a support ticket for an accurate diagnosis.
But, what I can do to try and help you @changil_shin is share some info that may help you in the meantime.
The SKIPFRAME log messages are generated when the Wowza Streaming Enigne does not have enough CPU/GPU resources available to keep up the transcoding process with the live streams. It is possible that your server has reached the maximum capacity and there are no more resources available.
Please note that the transcoding process is highly CPU intensive. In order to get an idea on how much CPU resources are needed to transcode a different number of incoming streams, into multiple output renditions, please take a look at the Wowza Transcoder performance benchmark article available here:
I would suggest you lower the number of incoming streams that are getting transcoded until you see a steady and consistent server behavior and no more SKIPFRAME messages are being logged in your server logs.
Also it is highly recommended to tune your server using the Performance Page in Engine manager for optimal performance and memory and here is the article on how to do that:
This article explains methods for tuning Wowza Streaming Engine for optimal performance on your hardware configuration.