[R2S Plus] [Upstream] Can't ping hosts connected to the same br-lan side

[Plaque-fcc]

Hardware: R2S Plus with RTL8822CS WiFi card.
Software: Linux 6.1.63 #1 SMP Fri Mar 29 11:26:33 CST 2024 aarch64 GNU/Linux; FriendlyWrt: OpenWrt 23.05.3 r23809-234f1a2efa / LuCI b07cf9dcfc37e021e5619a41c847e63afbd5d34a branch git-24.088.58402-5be51dc.

I configure a 5 GHz wireless interface phy0-ap0 without client isolation.
I connect three wireless clients to this AP,

1. I can ping the AP IPv4 address from these clients.
2. I can ping the clients from the router CLI via SSH.
3. I can access the internets with this router.
4. For some reason, I can't ping one client from another on the same br-lan network, on the same phy0-ap0 AP.
5. Additionally, I can ping between eth1 and wlan clients.

What may be the cause of this problem?

[Plaque-fcc]

Update: openwrt/openwrt#8159