X96max plus WLAN IPv6

I have an x96max+ box with S905x3 SoC.
I enabled IPv6 from sysctl. And ethernet interface works.

However, for wireless interface, it cannot get router advertisement. From tcpdump, I can see there are ICMPv6 Router Solicitation going out from wlan0 but no ICMPv6 Router Advertisement coming in. At the same time, I have a desktop monitoring the whole network and it confirms that the router gives correct router advertisement.

In brief, the network protocol stack of the operating system works fine, ipv6 works on eth0, but not on wlan0. I am suspecting that there could be something wrong with the wlan driver?

Here goes the wlan card info. seems to be Realtek RTL 8822CS.

CoreELEC:~/.opt/etc # udevadm info /sys/bus/sdio/devices/sdio*
P: /devices/platform/ffe03000.sdio/mmc_host/sdio/sdio:0001/sdio:0001:1
L: 0
E: DEVPATH=/devices/platform/ffe03000.sdio/mmc_host/sdio/sdio:0001/sdio:0001:1
E: DRIVER=rtl88x2cs
E: SDIO_ID=024C:C822
E: MODALIAS=sdio:c07v024CdC822
E: SYSTEMD_WANTS=rtkbt-firmware-aml.service
E: TAGS=:systemd:

If I configure wlan0 ipv6 address manually, it works and can connect to outbound ipv6-based internet. So, just RA not working.