After openwrt boot on RPi4 (lan on native ethernet port, wan on usb lan adapter plugged in to usb 3.0 port), tried to get speedtest (at dslreports.com/speedtest) which during the test the connection interrupted (error) and login to LuCI -> interfaces I saw "device is not ready" on wan and wan6 interface.
Tried directly connecting the usb lan adapter from laptop to ISP modem (using usb 3.0 port also) got similar result after trying speedtest or any activity which stress bandwidth. the network adapter became dissapear before reappearing again few times. At first I thought faulty USB adapter, but after some browsing and found several similar case with this chipset which probable cause is usb autosuspend on USB 3.0 port and one of the solution is by disabling it in linux or windows, I first tried disabling USB autosuspend in device managers. It helps a little now device only dissapear and reappear during upload test.
Then I try downloading RTL8153 latest drivers (windows 10) in realtek website, enable the USB autosuspend again, and try speedtest... no error or whatsoever after long usage.
I also tried using the USB 2.0 port on Rpi4 and test it again, also no error, but since the USB LAN Adapter is USB 3.0 Gigabit LAN so the speed drops considerably when using USB 2.0 port.