Well, I'm very happy to announce my system is now at last 100% functional!
I'm ashamed to tell I had Cubase 6 installed on both WS's tested. It was the previous necessary Steinberg Eucon adapter which took control on EuCon and made it go bananas wether running PT or Cubase
Uninstalled Cubase 6 + Steinberg adapter. EuCon is up running stable and better than ever both with PT11 and Cubase8.5.
Thank you so much for all your help and patience! Fantastic!