Deco Satelites (M3W) Cutting WiFi speeds in half or slower
I'm currently using a Deco M4R in "access point" mode which is wired into my AT&T router/modem combo with an ethernet cable. Along with this I have two (2) Deco M3W satellites plugged in. One satellite unit is less than 20 feet away from the main M4R, down an open hallway with no obstructions/walls/etc in the way. The second satellite unit is down the same hallway another 20 feet or so, again with no obstructions, all on the same floor of the home.
I have "AT&T 1000" gigabit internet speed here. The WiFi on my AT&T router/modem is turned OFF. The only WiFi in my home is the Deco WiFi.
When connecting to the main Deco M4R unit, I am getting solid download speeds between 400-600 Mbps. Those speeds are relatively consistent and apply when a device is either wired or connected to the M4R via WiFi. I have tried multiple devices and the speeds are good no matter what I test with (iphone, playstation, PC).
However, when connecting a device via WiFi to either of the two satellite M3W units, the speed drops to between 65-115 Mbps. I cannot figure out what the bottleneck is here. This slower speed is consistent across different devices including an Android tablet, an iPhone, and a PC.
All firmware for all of the Deco units is up to date. I have tried rebooting. I have tried unplugging from the walls and plugging back in. Nothing changes.
TP-Link's official troubleshooting fix for this is to "move the satellite Deco closer to the main Deco, ensure there are no/fewer obstacles between the main Deco and satellite."
Considering my satellite units are literally 20 feet from the main Deco and have NO obstacles or walls between them and the main Deco, I believe there is something greater at play here.
Any advice would be greatly appreciated! Thanks in advance.