Offline lets you open Pro when not signed into a Portal, but, if any of you data that is being access by the script is in a portal (and is not public) , will still need to log in to connect to the data itself.
That is what I was thinking "may" be going on.
Otherwise, I'm no help on the offline license thing. Tried it once, got disconnected, and was several days working with tech support before I got Pro working again.
On that same note, the last user that logged into Pro (under that windows account running the script) seems to be the credentials that it caches. I have had some of my scripts fail when the last username logged into Pro is a user that doesn't have creds to run the script(s). I have to log out of Pro, then log back in with proper credentials. Then, it will stick for two weeks, or until someone else logs in.
R_