Yep,,,solid working here ,,,AC86U Main and AC68U AiMesh node both are 384.18. I am little hesitate to go to 384.19 now as reported many issues thus decided to stay with 384.18 as it's been stable for months now until....Since I decided to dust off my AC68U and try it out as an AiMesh node, both the router and node have only used Merlin firmware. I haven't used ASUS' stock firmware for years.
My AC86U was on Merlin 384.17 when I first added the AC68U as a node, so I updated it to that version, then when 384.18 came out, I updated the router and node to that version, and now both are on 384.19. No issues with my mesh setup on any of these Merlin versions in my environment.
Imagine ,,,couple hundreds dollar Wifi router runs great 4+ years !!! (AC68U 4+ years old ,AC86U 6 months old and covering all house with Wifi 2.4/5Ghz full speed ahead with WAN 500/500)!!
I like stability!