Clients in same WLAN can’t reach each other

Still experiencing same problem as Clients in same WLAN can't reach each other, with OpenWrt 19.07.2 on a Buffalo WZR-600DHP.

With default settings ("Isolate clients" unchecked), clients cannot 'ping' each other and Chromecast (which relies on multicast) is very unreliable.

@jow's workaround from Clients in same WLAN can't reach each other still works (and is necessary) to enable inter-client communication:

config interface 'lan'
        option multicast_to_unicast '0'
config wifi-iface 'default_radio0'
        option isolate '0'

I have added detailed technical information to the bug report, including 802.11 packet captures showing that the default settings ("Isolate Clients" disabled), which relies on Linux kernel bridge hairpin, does not properly hairpin the traffic:

I would like to ask devs to kindly re-consider the priority on that bug.

I'm using .3 on three APs, and have three Chromecasts, no issues whatsoever.