Red Light when no monitor

[still creek]

I have a AK3 mini pc. I use it as a server, so I don't need/want a monitor attached. When I attach a monitor, all is well. When running without a monitor, I get a red light after running for a while. I tried using a dummy HDMI dummy plug. Same problem. When the pc light is "red", the server is still working and I can access it. After accessing the server, the light then turns back to blue.

Any idea of the cause and how to fix?

[admin]

Hello. The computer has entered sleep mode. It is recommended that you enter the system to turn off the sleep mode or change the sleep never to sleep.