Here the details about my cubox i4 which also had network issues with 5.8.x. It is currently running smoothly with an older version. I hope somebody helps this information as such driver issues go beyond my knowledge.
cat /etc/armbian-release
# PLEASE DO NOT EDIT THIS FILE
BOARD=cubox-i
BOARD_NAME="Cubox i2eX/i4"
BOARDFAMILY=imx6
BUILD_REPOSITORY_URL=https://github.com/armbian/build
BUILD_REPOSITORY_COMMIT=b9814056
DISTRIBUTION_CODENAME=buster
DISTRIBUTION_STATUS=supported
VERSION=20.11.3
LINUXFAMILY=imx6
BRANCH=current
ARCH=arm
IMAGE_TYPE=stable
BOARD_TYPE=conf
INITRD_ARCH=arm
KERNEL_IMAGE_TYPE=Image
uname -a
Linux <hostname> 5.7.15-imx6 #20.08 SMP Mon Aug 17 07:36:36 CEST 2020 armv7l GNU/Linux
find /sys -name phy_id
/sys/devices/soc0/soc/2100000.bus/2188000.ethernet/mdio_bus/2188000.ethernet-1/$
find: ‘/sys/module/at803x/drivers’: Input/output error
ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet <ip router> netmask 255.255.255.0 broadcast <ip cubox>
inet6 2001:9e8:208c:6800:84e5:8994:7642:4da2 prefixlen 64 scopeid 0x0<global>
inet6 fe80::3721:95e0:891b:d0ef prefixlen 64 scopeid 0x20<link>
ether d0:63:b4:00:32:d9 txqueuelen 1000 (Ethernet)
RX packets 17508632 bytes 3075857589 (2.8 GiB)
RX errors 0 dropped 4 overruns 0 frame 0
TX packets 6162802 bytes 803661074 (766.4 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0Cubox