Disabled state stopping other states from appearing

You said, 

I've set up the trigger 'set state of button 1 to visited when user clicks button 1'

I wouldn’t expect this to work, because the disabled state means the object will ignore clicks. 

There is a sample that does what you want at this thread:

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

Use the Restricted Navigation.