My internet speed dropped to ~200mbps from ~900mbps after I upgraded my AC88U from 384.19 to 386.1. Not sure if this helps, but I am using aimesh (with 3 AC66U B1, all updated to the latest stable version available on ASUS's website, and am running an OpenVPN server, have guest network enabled, using link aggregation and using port forwarding. I tried downgrading my aimesh nodes to merlin 384.19 while my main router (AC88U) is on 386.1, but this does not help. My LAN speeds are unaffected. Not sure if this is a bug?