Slow Wifi Speeds using RBR50 and 2 RBS50 satellites

[toxster]

I am running a Mesh system with a RBR50 router and 2 RBS50 satellites. Running latest firmware (I have checked for updates to confirm they are up to date). My cable internet connection is through Spectrum @ 400 Mbps. I am using a modem only (it is NOT a wifi router) so this is not a double NAT problem. Until a few weeks ago I consistently got 400+ Mbps on all my devices when using Speedtest over wifi. I noticed a slowdown so I checked and now I am only getting 30-40 Mbps. I did a speed check from the router using the Orbi app and it is showing a full 400 Mbps, so the problem isn't there. My desktop is plugged into the ethernet port on one of the satellites and it gets a full 400 also, so the problem is not with the backhaul either. I have tried checking and unchecking MU-MIMO, Beamforming, Daisychaining and there is no improvement when these are either on or off. I have tried speedtesting my devices in different parts of the house (approximately 3800 sq ft) and it is the same everywhere. Obviously I have rebooted the router and the satellites. I am at my wits' end. I searched the community without finding any solutions. Any help would be appreciated.

[FURRYe38]

v16 would be most current FW.

Has a factory reset and setup from scratch been performed since last FW update? 

What is the distance between the router and satellite(s)? 30 feet is recommended in between RBR and RBS to begin with depending upon building materials when wirelessly connected. https://kb.netgear.com/000036466/How-far-should-I-place-my-Orbi-satellite-from-my-Orbi-router

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Try enabling Beamforming and MIMO(MIMO may or may not be needed) and WMM. Under Advanced Tab/Advanced Settings/Wireless Settings

Try disabling the following and see:
Armor, Circle, Daisy Chain, Fast Roaming, IPv6 and Set 20/40Mhz Coexistence to 40Mhz only. Set Short preamble instead of Long preamble modes. Save settings and reboot the router and satellite(s).

One User Experience/Configuration:
https://community.netgear.com/t5/Orbi/Most-Stable-Orbi-Configuration/m-p/1941087/highlight/true#M970...