How come I can't get the triggers to work on the last slide?

There's probably a conflict between the variables and disabled states. You don't need the variables because you can track by state change.

Here's what I'd try:

• Delete the trigger to change next button to disabled (you don't need that)
• Change the initial state of the next button to hidden
• You don't need the variables triggers.
• Change the state of the next button to normal when the states of all of the objects are disabled.