Odd State Behavior in LMS...

I'm stumped and hoping someone can help. I've not been able to force this to recreate. 

I have a course in which there are slides that include navigation buttons allowing the learner to choose which topic to get more detail about first, second, third... I want to give them the ability to interact somewhat while still making sure they get all the info. 

The buttons show layers and there's a variable that changes at the end of the audio on each layer which changes the state of the button. After the buttons are all in the Complete state, the Next button will appear allowing them to continue. 

Sometimes, and only sometimes, the Complete state will disappear from one of the buttons. Then it will reappear then it will disappear. It's very strange and unpredictable behavior. I've discovered if a person clears their cookies during the course it'll cause issues but this happens without clearing cookies or anything. 

These are all people working remotely, different networks, different kinds of computers, etc. The only common denominator is the LMS which is Cornerstone. I'm wondering if anyone here has experienced anything like this or can see something I'm doing wrong in the slide I've attached before I go to Cornerstone with it. 

Thanks so much!