Button not becoming visible

Using states in the "When" part of works if you are just visiting layers on the same slide, or initiating actions on the same slide. when you start visiting other slides, depending of state changes generally works out like, well, you can see how it works out. Another problem, for me at least, is that the visited indicator shows up as soon as the button is clicked, and flashes before the slide jump is made.

To visit other slides, keep track of which ones have been visited, and show a button when they have all been visited, you really need some industrial record keeping. The states aren't up to the task, but variables are.

Check the mixed navigation in the sample at this post:

https://community.articulate.com/discussions/articulate-storyline/free-sample-restricted-and-free-random-navigation-using-variables-and-triggers

It allows the learner to choose which path to follow, marks it as visited on the return, and shows the Next Unit button when all have been visited.

I think it will work perfectly for what you want.