Lois,
As a few debugging steps, I received the new i5 NUC BOXDC53427HYE and swapped out the memory, mSata and the wifi + bluetooth. Started it up and did a speed test and the network is back up clean and reports back the full 20 Mbps of the internet connection.
On the defective unit, I tried clicking on the speed test when the lan was connected and removed the hdmi and waited for a logical end point and saw the speed had not increased.
My findings are that the network unit can get defective. I hope this does not get spoilt as well.
Let me know if you need any assistance. Thanks for looking into it.