Unfortunately, count me in the camp of users that needs to downgrade...
My setup and config - AX88U as Wireless Router and AC88U and AC68U as Media Bridges.
AX88U - separate 2.4 and 5Ghz SSIDs, fixed channels (48 for 5Ghz, 9 for 2.4Ghz). 2.4 is on the 20/40 setting, 5Ghz is 80Mhz.
No QoS, running spdMerlin, amtm and scribe. 5 devices hard wired, around 16 clients on 2.4 band and around 18-20 on the 5Ghz. 2 of the 5Ghz devices are AX200 based (so 16 AC and 2 AX). My ISP (Spectrum cable) provides 100 down, 10 up via an Arris SB6183 cable modem.
What the issue was is a gradual decay of upload speed to the point it almost stops. Download appears to be fine. Its so bad, even DNS requests can fail. Here is a graph from spdMerlin showing a typical 24 hour period running 384.15:
After numerous tests, the only way to get back to "normal" is a reboot of the AX88U. I have done the factory reset and restored my settings by hand - no change.
After ~a week of this, I re-installed 384.14, did the factory reset and settings. It has been approx 24 hours and it is running much better. Here is a spdMerlin graph running 384.14
All I can suspect at this point is the newer Asus code merge in 384.15 for the AX88U.
I noticed 384.16 Alpha is out - and from Merlins comments will be using another Asus merge. I will try that once the new Asus code is merged...
I really liked 384.15. The promise of OFDMA along with better amtm/Add-ons was great!