DIAGNOSIS This is almost always a backhaul problem. The satellite talks to the router wirelessly, and if that connection is weak or on a crowded channel, your device's speed at the satellite suffers. It's using the same airtime to talk to the router and to your device.
FIX First, check the connection quality in the Orbi app. Tap on your satellite—it should show a "Great" or "Good" connection to the router. If it's "Fair" or "Poor," the satellite is too far away. Move it closer to the router. Second, log into the web interface at orbilogin.com. Go to Advanced > Wireless Settings and try changing the Backhaul Connection Priority to "6GHz Preferred" if you have the RBKE963. This forces the satellite to use the faster, less crowded 6GHz band to talk to the router.
IF THAT DIDN'T WORK The ultimate fix is to run an Ethernet cable from the router's LAN port to the satellite's LAN port. This creates a wired backhaul, which is faster and more reliable than any wireless connection. Once connected, the system will automatically use the Ethernet for backhaul.
HEADS UP Don't judge satellite placement by WiFi bars on your phone. Judge it by the satellite-to-router connection quality in the Orbi app. The ideal spot is halfway between the router and your dead zone, not necessarily in the dead zone itself.