@ LouisCpro - But the new SDK wasn’t released some weeks ago? 
Oups !
Did not see that your last post was as recent !
I’ve tried the same sample as your with my G120HDR board, and did not have any problem, considering however that I had to replace the Main() with another implementation that Initialize my ENC28…Effectively, the given code sample did not change from the “Pre-Gadgeteer” period, where fixing IP was mainly done using MFDeploy in a static way…
This means that the problem is not on the SDK anymore, but more on another part of he project…
Reading again all your post, I would first suggest to fix a static IP instead of using DHCP, and try it again…
It is possible that your error comes from opening the socket while the IP Address is not even correctly SET !