Timeline trigger not working...but only for some users

I have a very simple "Right to Know" compliance course that consists of a title page, a video page, and a completion page. I have the next button set to be disabled when the timeline starts on the video page, and I have another trigger to turn it to "normal" after the timeline reaches 624 seconds (10 minutes, 24 seconds). The video is 10:24, and I have the trigger in place to ensure that the users view the whole video. 

A handful of users are experiencing an issue where the next button is not triggering back to normal. Some have claimed to have watched the video 2-3 times or have waited on the screen for an extra few minutes, waiting for the next button to change over, but to no avail. Most users are not experiencing any issues.

I'm basically recycling this same course from the past two years and have just updated the video. Previous years have not had this issue at all. The triggers all look correct to me. What am I missing?