Thank you for your answer. 

If you haven't already, I suggest checking that there isn't a difference in your Go setup, by working out the "go run ..." command that is being run below, and running that manually yourself.

My first assumption was - to be honest, still is - that the "go run …” is not executed at all because the call to “go run …”  is within an illegal elisp function. Am I wrong with my assumption?

Kind regards
Mario

P.S. Would have no idea how to work out what the outcome of the function is ;)