Problem device: Tp-Link Archer C6 v2 EU version Software:
I installed the open wrt binary using this guide: https://radix007.github.io/OpenWrt-Tp-Link-C6/#installing-openwrt-using-tftpd-method-b-
No custom setup was done, I only turned 5Ghz radio on. Both wifi and ethernet worked out of the box, WAN connected without issues however in the morning internet connection was down. It fixed after restarting WAN interface from GUI. According to my script that was pinging google connection lasted for about 7 hours before going down. There were no logs from around the time connection was lost.