Orbi Router(RBR50) low speed than satellite (RBS50)

What FW is currently loaded?
What is the Mfr and model# of the ISP modem the NG router is connected too?

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

Besure that when you testing wifi speeds that when you move from one location to another, turn OFF the wifi on the testing wireless device, then move to new location, then turn ON the wifi on the wifi device and then test. You maybe testing speeds while your device is acutally connected to the satellite, then when you move near the ruoter, the device is still connected to the satellite, thus seeing a small degrade in speed. You have to get the device to disconnect from the satellite and re-connected to the router before testing speeds. The device will not automatically disconnect based on signal conditions. 

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.