I’m also still able to reproduce on a factory reset to the 3.027 firmware. I sshed onto the clean router and used uci set to mark the wireless config changes. Restarted the router, verified the wpa_group_rekey and disassoc_low_ack settings took effect. Then again I connected 8-12 devices (~3 Android phones, an iPhone, a macbook, ~6 iPads, and a zebra printer). Within about 5-10 minutes I was back in the broken state.
logread is still showing the “deauthenticated due to local deauth request” hsotapd messages with a lot of dnsmasq “failed to send packet: Resource temporarily unavailable” messages mixed in. 2.4G still seems unaffected.