Orbi Wired Speeds Unacceptably Slow - Wifi Not Impacted - QoS Issues?

So I have had a very similar but slighty differn't problem to the OP I think.

My Orbi has been working fine for WIFI, well not actually I've been plagued with problems, once I had solved all of them though I was getting a good speed on  my wireless devices. My Wired desktop however would be fine (214 down, 21 up) but after a random amount of time I would notice my connection had slowed and a speedtest would only show 5-7 down but still 21 up. 

If I restarted my desktop the problem would go away, for a time. I presumed this was something to do with the DHCP lease from the router but I'm not an expert. 

I was reading this post today because I am getting really fed up with it now and tried ThePenguin's suggestion to check the Speed & Duplex value for my connection in Windows. It was already set to Auto Negotiation for me so I changed it to 1Gps, because why not. The problem imidiatly went away, now maybe changing it restarted the connection and gave my desktop a new lease or just did the same as whatever restarting my computer was doing before but it doesn't seem to have come back for a while. I'll update if it does

I have to add, I paid a lot for this Orbi system and it really hasn't lived up to expectations so far. Every other router I have had has worked out the box perfectly and then I have tailoured to to my wants. This system which cost a lot more then them as not worked well at all out of the box and the options we are given on the configeration page are woefully inadequate. I was thinking about getting Google Wifi but thought it would be better to go with Netgear because they know networking and would give me lots of options to tailour my router how I want and need it.

Seems I was wrong on both counts!

Harware Version - RBR50

Firmware Version - V1.8.0.6

WIN10 64bit

Asus X99 A-2 Mobo