Navigation where users cannot advance until the timeline is complete

I didn't take a long look, but here's what I think is happening. 

When you jump back after viewing the slide and it's set to resume state, the slides starts at the end and timeline never really gets to move.

However, you have a trigger to disable the next button. But since the timeline is at the end, it never does anything. And you locked the slide so the user can't move the  seekbar.

I'd set the slide to reset to initial state. And then use a variable to track if the slide has been visited. Then set the trigger to change the state of the next button to hidden when timeline starts on the condition the slide hasn't been visited (which you know from the variable).

This way, the first time it's all locked, but afterwards, the next button is available and the slide plays as you want it to.