Was supplied a new modem from ISP (a TP-Link VX420 G2H) Unable to get bridge mode recognised by my RT-AC86U so just disabled wifi, DHCP on modem, and connected a LAN port on modem to WAN port on router. The result is that I have no internet on the 2.4Ghz and 5Ghz wifi, but do have internet on the 2.4Ghz guest wifi. I'm running Merlin firmware 386.11 and don't really know where to look to solve this.