Ok, I've mentioned some strange behavior with my more complex setup of using an 86U as the Wireless router, connected to a 68P as media bridge, and now a 3200 as AP (replacing a 66U as of today). I thought that there was possibility of the 66U being on the 380 firmware causing the issue I'm seeing, but think otherwise now having replaced it.
I have ~35 devices connected, most on 5GHz on the (now) 3200 AP, however they will intermittently drop internet for about 10-20 minutes during the day only to restore connection with no user intervention. When this occurs, the router, MB, and AP will show entering and exiting promiscuous mode in the logs and when that stops, the connection is restored. On a Windows 10 client or mobile, I can see the WiFi connection, but the IP address is lost and sometimes the connection disconnects and reconnects several times, but this appears to be dependent on the device (Windows, Android, Amazon Echos, etc.). Again, no restarts are needed and this happens randomly throughout the day, but does seem to be an issue that is no solvable by restarts, factory default and reconfigures (have done so more times than I care to admit) or by eliminating variables, e.g. custom scripts like AB-Solution, Spynet, OpenVPN, dnscrypt, etc.
Is there a general thought that 384 and above have a wireless connection stability issue outside of a single device in router mode or based on number of clients? Any thoughts on how I can help troubleshoot further or help the community with what I've done my best to isolate without success?
I had the same issue with an ac88 as my central router and two ac68 as repeaters. I enabled logging and and absolutely sure that you wipe the config on every device and configure from scratch. I had to do that multiple times. Then enable debug logging and check and see if they show anything for the period of time you lose network connectivity. I found quite a few devices go in some sort of DHCP loop over and over. I moved those to 5ghz ssid and now everythings been relatively stable.