Interesting. I have a similar setup (except with 2 aimesh nodes). I will try a complete reset later tonight and try again.Also running an RT-AC5300 as master router in an AIMesh configuration with three RT-AC68U units as nodes, wireless backhaul, currently on 386.1_2 no major problems. I did have a problem after one dirty update back when I was running 384.19 in which the router would reboot every few minutes. I did a factory reset, completely nuked everything, and reinstalled from Recovery Mode. That resolved the rando reboot issues for me. Since then, I've updated several times, including from 384.19 to 386 and beyond. All of those updates have been dirty, and the router has remained stable thus far, as has the AIMesh configuration. I also had one update in which the UI was sluggish immediately post-upgrade. That condition resolved on its own after about an hour of uptime...most probably after the router completed a database update. All I can add to the conversation is to agree with New2This in suggesting a total nuke of the router, and a clean reinstall and hand reconfiguration.
Thanks for the feedback.