I'm on my second RT-AX88U since the first one was dropping lan connection to my PC and I've returned it and got a replacement, but since a week ago the new router started doing the same. It randomly disconnects my PC and all other WiFi and lan devices are working fine. I've replated the cable with a brand new CAT6 cable tested with Fluke. I've also changed my lan card to the Aquantia 5G on my motherboard. I even tested with ASUS 10Gb Lan card and the onboard Intel 219 but the problem persists.
I'm not using AiProtection, Adaptive QoS, Traffic Analyzer and Game Accelerator features. I also disabled the Jumbo Frames.
I really live the RT-AX88U, because of the 8 lan ports, but this is getting very annoying. I'm also using ports 1 and 2 in Link Aggregation to my NAS and my PC is attached on port 3. I also have 2 IP cameras and another PC attached with cables to the router. I'm using the latest firmware on the router and did a reset already, but that did not change anything.
Edit: Here is the system log from the router:
Apr 17 15:43:53 kernel: eth2 (Ext switch port: 1) (Logical Port: 9) (phyId: 9) Link DOWN.
Apr 17 15:43:56 kernel: eth2 (Ext switch port: 1) (Logical Port: 9) (phyId: 9) Link UP at 1000 mbps full duplex
Apr 17 15:45:20 miniupnpd: HTTP Connection from 192.168.0.73 closed unexpectedly