Great as always thanks Merlin.
Surprisingly I found RT-N66U_3.0.0.4_374.35_4 quite buggy, minidlna would not work and sit in idle no matter how many reboots, 5Ghz WiFi would drop intermittently and require a reboot, and internet connection would also take a long time to reconnect. I downgraded back to RT-N66U_3.0.0.4_374.35_2 and everything seems to work well again, except in OpenVPN Client, when adding certificates in Content modification of Keys & Certificates does not seem to save no matter what. Anyone else have the same issue?
There has been zero changes outside of OpenVPN and one DualWan loadbalancing firewall change between 35_2 and 35_4.