PixelStreaming inoperative after a certain time.

Hi there~
After a certain period of time, pixel streaming does not work with the following message in the web browser:


The error message from the signature server is as follows.

The signing server code used the default code provided by Unreal.
(C:\Program Files\Epic Games\UE_4.25\Engine\Source\Programs\PixelStreaming\WebServers\SignallingWebServer)
It works well for the first few hours, but it doesn’t work when you click on the browser after a certain amount of time has passed.
As you can see, there is nothing special about the signature server’s message.

The same problem occurred when I tested it with a very simple scene.
Is there a node that needs to be implemented specifically when creating an unreal app for pixel streaming?
Or should I modify the code of the signature server?

If anyone has experienced the same problem or solved it, I would appreciate it if you could give me some advice.