Hi
Thank you for sharing your experience. It is possible that certain devices are having issues with Wi-Fi broadcast/multicast support.
You can consider SSHing into the router and running the following commands to see if they fix the issue. Modifying the kernel parameters directly like what you have done is also a valid approach.
# Enable the Proxy ARP
uci set wireless.wifi2g.proxy_arp='1'
uci set wireless.wifi5g.proxy_arp='1'
uci set wireless.wifi6g.proxy_arp='1'
uci set wireless.wlanmld2g.proxy_arp='1'
uci set wireless.wlanmld5g.proxy_arp='1'
uci set wireless.wlanmld6g.proxy_arp='1'
# Enable the Multicast to Unicast
uci set wireless.wifi2g.multicast_to_unicast_all='1'
uci set wireless.wifi5g.multicast_to_unicast_all='1'
uci set wireless.wifi6g.multicast_to_unicast_all='1'
uci set wireless.wlanmld2g.multicast_to_unicast_all='1'
uci set wireless.wlanmld5g.multicast_to_unicast_all='1'
uci set wireless.wlanmld6g.multicast_to_unicast_all='1'
uci commit
reboot