Have you changed the settings on the ps4 after you installed the router? Make sure the MTU matches on both console and router.
Before you try anything go to the asus website and get the latest firmware, the one you're using might be a year old.
Its original firmware so you will still be able to leave t back and if you get it working then you can put CFW on if you like.
CFW Custom Firmware, its made by enthusiasts for free which are sometimes better that the manufacturers stock firmware. You can revert back by doing a factory reset.
I dont see firmware 18.104.22.168.374.39 which yours is
Mine currently is 22.214.171.124.276
I think the latest version on website is 126.96.36.199.374.4561
What should I do - is 188.8.131.52.374.4561 okay?
ta for your help
Mine is cfw by Merlin.
I tried it on the asus fw before I put the Merlin fw on and it was lag free. Try it with the new asus fw and if it doesn't work try tweaking the up and download limits with QoS. I have also changed the dns server on mine, you can try that but I'm not sure if that will make a difference.