Orbi RBR850 WiFi extremely slow

[Flighthawk]

My setup is an Arris Surfboard 8200 with no WiFi, Cox 1Gbs service and a Orbi RBR850 with two Satellites.  I recently noticed when trying to download some magazine subscriptions on my iPad that it was extremely slow.  I ran a speedtest on my iPad Pro and was getting under 20Mbs.  I then did some testing on my iMac which is 5' from my Orbi router.  A speedtest on Ethernet (connected to the router) was 928/33.3 Mbs, but on WiFi, it was only18.3/16.2.  

I've reset everything with no changes. I did some searches and made sure that IP6 is off, tried various channels, no Armor, no parental controls, etc, etc, with no changes.  Since setting up my Orbi about a year ago, I have made NO changes to it.  After initial setup, WiFi was in the 400-500Mbs speed, now it's 1/20th of that. Could it be related to an automatic FW update?  Current FW is 4.6.3.15.  The system was purchased from Netgear in May of last year so is now out of warranty.  Can't ask Netgear support for help without purchasing a 6 mo $90 service contract.

I'm at a loss at what to do.  Every wireless device connected to the Orbi is seeing these slow speeds, not just one.  Suggestions would be greatly appreciated.

[Flighthawk]

Update #1:  My MacBookPro shows it's connected via 5GHz on channel 48.  Speedtest is under 20Mbs.  So problem is not related to 2.4GHz.  Will see if I can factory reset entire Orbi system and reconfigure.

[Flighthawk]

Update #2:  I decided that before I attempt a reset and fresh install, I'd play around with some of the 5GHz advanced settings.  First, I turned on 5GHz WMM with no affect.  Then I turned preamble from auto to short and the speeds jumped from 18Mbps download to 281Mbps. Have most of my speed back and I'm not touching anything 🙂

[FURRYe38]

What is the size of your home? Sq Ft?
What is the distance between the router and 📡 satellite(s)? 30 feet or more is recommended in between RBR and RBS📡 to begin with depending upon building materials when wirelessly connected.

Here my Mac Book Pro speeds at 1300Mpbs connection rate: OSX 12.0.1

My 8 series current settings and configuration:

https://community.netgear.com/t5/Orbi-WiFi-6-AX-and-WiFi-6E-AXE/New-Online-Update-4-6-3-16-RBR850-RB...