I looked at it too and didn't find anything clear.
The session location is what seemed to fail:
"javax.script.ScriptException: ReferenceError: "sessionLocation" is not defined in at line number 1"
Was it possible that the supervisor was speaking for a period of time where there was no activity, then asked the users to go to a new screen? You can figure this out by looking at the times in the log before 12:16 on 9-22-17. Was there a significant delay before then?
Also, @dkayiwa Do you know why there's a save user action logged each time the page is viewed?