Having a bit more success with it now.
Think I figured out an issue:
When OSBot is loaded, it defaults to a members world. If you don't select a f2p world prior to starting the script, it will attempt to log in, and then terminate the script when it fails.
When you change the world, then load the script again, it will log in ok, but the issues arise. It feels as though 2 copies of the script are running at the same time.
Stopping the script and restarting it seems to fix the issue.