Archer C7 V2 - Traffic not working between some LAN hosts

[sammo]

You have hit this problem

Archer C7 2.4 GHz wireless dies in 24~48 hours

TP-Link Archer C7 v2, OpenWrt 18.06.4 r7808-ef686b7292 Every 24~48 hours on the 2.4 GHz WiFi, network starts to crawl, has high ping times and then just dies. It may come back but most of the time it stays dead. A router reboot fixes it for another day. Ethernet connections are fine. There is no time of the day or particular sites that do this. How do I debug the issue?