@RemcoD 

Hello, please help confirm some details and we can try to fix it together. 

1. What is the current network diagram? How many Deco M9s in your network? How are they connected?

2. Do you mean the LED on the Deco M9 will blink red when the PS4 loses the connection? How about other devices connected in the network, are they experience the disconnection issue? Generally, if the LED on the Deco M9 blinks red, it means the internet connection on it is broken, and there won't be internet access if a device is connected to the Deco network.

3. What if you leave the PS4 disconnected from the Deco network, will there be an issue?

Thanks.

@RemcoD 

Hello, sorry to respond late.

Try to disable fast roaming on the Deco system, and ensure there is no IP conflict in the local network. Is the PS4 using a static IP address? If yes, try to change its IP address to another one to give it a shot.

As I mentioned earlier, is the LED on the Deco M9 is flashing red, that means that Deco M9 is disconnected from the Deco network, can you confirm again are other devices connected to it can still get internet access? Or there are no other devices connected to it?

Thanks.