Video not marking activity complete

Summary

Videos are not marking complete

Content

At times videos are not marking the activity as completed for our Learners. The issue is not consistent with a browser or with a video. Sometimes the Learner watches the video more than once from the initial launch or relaunches it and it marks it complete. At other times, nothing seems to mark it complete other than an Admin. 

Has anyone had this issue? Or know what we can do to rectify it. It's been ongoing since we implemented in 20B.

We have tried, to delete the activity and recreate it, and reloading the video to Catalog Resources to create another activity.