I noticed that every time I plugged my MacBook Pro or Air directly (via USB C)  into my newly purchased backhauled X50 Pro Access Point the speed drops to ~450 Mbps.
 

If I plug the MacBook directly into the Ethernet port in my wall, speed was back up to where it should be (2 Gbps) . After a few hours of trying to troubleshoot this, it appears that when I have my second USB C port connected to an external Dell monitor, the speed drops by 1/3 or more but if I unplug the external monitor the speed jumps back up to where it should be. I've tried two different USB C to HDMI connectors/cables (Anker and Ugreen).

At this point, I'm better going wireless (~900 Mbps) to my main Deco.
 

I'm not too technical but there is some conflict with the Deco and the USB C port behaviour that goes away if I unplug the second USB C portused for my external monitor  or I plug directly into the ethernet port on my wall - in which case I can have both USB C ports active or as mentioned go wireless.