Asus rt-ac66u wifi problem. 1 unit loose connection

[Syklitengutt]

I have put my router from supplier in bridge and disabled dhcp so my asus takes care of everything. It is set up with pppe0 and everything works nice except on 1 phone a Samsung s7. It connects fine but after some time the net dies and I can't access any webpages. I can't even access the router trough wifi. The router I have tried with standard firmwire but now runs merlin firmware. I have computers and 2 other phones connected to same router without any problems. This is driving me nuts. On my phone I have wiped all remembered networks. If I set a static in address on my phone it works for a short time then stops. This is all on the 2.4 GHz frequency.