Storyline course completion issue with Cornerstone in Demand

Hello all, we've been publishing our online courses in SCORM 2004 3rd edition and we're having a few people having completion issues accessing them through Cornerstone OnDemand. For most of the cases we've seen, the users claim that they've completed the course already through the basis for completion (pre-assessment, final assessment) but for some reason, the LMS does not mark them complete. Upon checking their course, they are bookmarked to go back either to the start of the course or in the middle of taking the quiz. Most common case is when someone passes the pre-assessment, where they would've been marked complete already. We are looking at a couple of potential causes like LMS timeouts, internet connectivity issues or network bandwidth issues, but checking here if we have any similar cases that might help us understand this particular issue. Thank you!