I'm sharing this in the hopes that possibly someone has a few miraculous fixes or suggestions or that Cisco will make their APs and AP Software more stable (fix known issues faster e.g. updates that "break" third-party certificates and in turn the 9800 Web Management GUI ), better performing, flexible and a somewhat user friendly (at least when using the Web GUI) than most consumer-grade APs or from competition (e.g. Ubiquiti, Aruba).
I have recently upgraded our corporate Wi-Fi from a EoL 5508 (AireOS 8.5.161) to a Cisco 9800-CL WLC platform using existing 1852i and some new 9120axi APs, biggest bugs among other was that guest Wi-Fi portal(s) wouldn't redirect properly (blank page) over time and FRA would cause SSIDs to only transmit on 2.4GHz despite the SSID only being 5GHz enabled (quelle surprise).
Like many techies, I managed to acquire a Cisco 3802i AP (£1000 plus 802.11ac AP) for my own home Wi-Fi Setup, deployment and testing for the above migration/upgrade. After more than a year of troubleshooting with the 9800-CL and the 3802i, I couldn't get much better than 802.11n (5GHz 300Mbps) speeds (Window Clients report up to 1300Mbps capable) from the 3802i when using the 9800-CL (IOS-XE17.3,17.6,17.8 and 17.9), furthermore, the 3802i would cause clients to drop-off for up to ~15 minutes at a time multiple times (at least twice a day) a day. over months of playing around with DCA, Channel Widths and FRS etc (Cisco WLC's Best and Maximum meanings are seemingly arbitrary and not literal!!)... settings I finally realized that the 1852i and the 9120axi APs (borrowed from work) didn't suffer from this client drop-off issue and the 9120axi was able to reach above 802.11n speeds, but sadly not reach true base 802.11ac speeds (i.e. 867 Mbps), I only achieved ~500Mbps (54 Megabytes Per Second (MB/s) in Windows SMB copy testing), this led me to think my 3802i might be faulty (still might be??). I even took it apart to look for the obvious bulging capacitor or lose aerial connections but visually I couldn't see anything wrong. Grasping at straws I went back to my old AireOS vWLC (think it was on 8.5.x 80+80 MHz) as I briefly managed to reach speeds of ~800Mbps (80 MB/s in Windows SMB copy testing) but in the process of moving to the 9800-CL is seems I messed up its config so I tried Mobility Express (ME) on the 3802i, while I didn't get 80MB/s I'm at least able to get up to 60MB/s "out of the box" no more drop-outs (weeks of operation now)... but using the ME GUI to tweak things like enabling 160MHz or 80+80 channel widths is broken (multiple users have asked this question for years if you search the web)... why does Cisco include these options as the ME GUI just gives so many useless unexpected error messages such as the "Configured DCA channels are in invalid combination for selected Channel Width." but then nowhere on the Web or Cisco documentation are you advise to correctly set DCA channels, even if you attempt by trial and error the GUI DCA settings don't seem work as GUI claims to apply channels but then refresh the page and your changes are gone/missing!... this is supposedly a supported mature 5 year old product line with the same known issues for more than 3 years, come on Cisco do better or kill the non Meraki Wi-Fi stuff if your not seemingly interested in it!!!
