Thank you @farouk.serragedine for your contribute! And welcome on the magical mistery tour of “extendsrf” 
Actually you hit one point: the original file was from a different CAD (solidworks, I reckon).
And your solution for sure helps as a workaround in Rhino 8 WIP.
But in my opinion this behaviour keeps configuring a bug or at least an unwanted regression from Rhino 7 which, concretely, is able to make the command work flawlessly on the same surface and on similiar ones.
Try executing the command on that surface with Rhino 7 and you will see you don’t need to do any preliminary operation: the command just works as expected.
Infact I had to go back to Rhino 7 for working on that file, whom original copy was sent to me by a client and has plenty of surfaces I need to work on, behaving like this one. And of course it doesn’t makes sense to me adding extra work with Rhino 8 where Rhino 7 makes it easy.
So, thank you very much again for your suggestion (it’s now officially in my “book of workarounds for Rhino weird attitudes” : ) but I would prefer this can be solved and Rhino 8 starts to behave like Rhino 7, in this cases.
What do you think @davidcockey ?7