When Connecting to Half Gigabit Internet with Ac86u, Upload Speed is Slow.?

Hi. I am a Korean user and I am using an AC68P. This time I bought an AC86U router. I am using the 500MB Internet (KT Giga Compact) provided by KT in Korea. The problem is that the AC68P has the fastest upload and download speeds for both wired and wireless connections, while the AC86U has a good download speed, but only half the upload speed. (480-495 MB / S download, 200-250 MB upload) The above problem occurs when the internet cable is directly connected to the WAN port of the AC86U. The peculiar thing is that if I connect the internet cable to the WAN port of my AC68P and the wire from the AC68P's LAN port to the WAN port of the AC86U, the download and upload speeds are the fastest. Wireless and wired perform best when the AC86U is operating in AP mode and when the AC86U is operating as an AiMesh node. (480-495 MB / S download, 480-495 MB upload) The AC68P's firmware supports Half Gigabit Internet, but the AC86U's firmware doesn't seem to. Can you solve this problem?