Next & Prev Button question

Here's my best guess: There's a "Set the state of the Next button to Disabled when the timeline starts" trigger. Then there's another trigger to enable Next when the interaction is complete. 

The problem is that a "when the timeline starts" trigger runs every time the user visits the slide. That's true even if the Slide Properties are set to "Resume saved state." 

The fix is easy: add a condition (or conditions) to the disable-Next trigger so it will only run if the interaction hasn't been completed. 

For example, if the interaction is done when a set of buttons = Visited, the disable-Next trigger would look something like this: 

Note: It's more stable to use "≠ (is not) Selected" or  “≠ (is not) Visited" as a condition, instead of "= (is) Normal." As Hero Walt Hamilton once put it: like us, every state thinks it's Normal. In other words, Normal underlies the other states, so the "= Normal" condition doesn't always work as expected.