SCORM is freezing when retaking the quiz.

I'm maintaining an LMS, and many clients are complaining about quiz slides that are getting stuck - happens only for SCROMs that were published via captivate (either 1.2 or 2004). Sometimes it's after retaking them, sometimes it's on the first attempt, and I have tried to debug many times to determine what the problems are. I need your advice: what can be the issue?
I suspect that is related to the suspend_data value.