Orbi losing speed between units

[Monica123]

Have 50 Mb download speed at modem.  Constantly fluctuating signal at both add on Orbi units, but never achieving more than 15 Mb downloads.  Have 3 units in 4500 sq ft house.  constantly having buffering coming on during all times of day trying to watch streaming shows.  fluctuating and sometimes on /off internet access in various parts of house....... suggestions???

[FURRYe38]

What FW is currently loaded?
What is the Mfr and model# of the ISP modem the NG router is connected too?
Is the Orbi system operating in Router or AP mode?

What is the distance between the router and satellite(s)? 30 feet is recommended in between them to begin with depending upon building materials.

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?
What WPA security modes are you using?

Try disabling the following and see:
MIMO, Daisy Chain, Fast Roaming, IPv6 and Set 20/40Mhz Coexistence to 40Mhz only. Save settings and reboot the router and satellite(s).

If you updated to recent FW v.210, try enabling Daisy Chain. Some have mentioned that this seems to be working in reverse order, enabling means disabled actually.